core: free the strings in the set as well during unit cleanup

Spotted while fuzzing #27890.

=================================================================
==908098==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 64 byte(s) in 1 object(s) allocated from:
    #0 0x7f4efe6d81f5 in __interceptor_realloc.part.0 (/lib64/libasan.so.8+0xd81f5) (BuildId: dc689b05ca2577037af24700212bb5cce1f91c8a)
    #1 0x7f4efb8e3ace in greedy_realloc ../src/basic/alloc-util.c:70
    #2 0x7f4efb93b713 in extract_first_word ../src/basic/extract-word.c:62
    #3 0x7f4efb970d50 in set_put_strsplit ../src/basic/hashmap.c:1902
    #4 0x7f4efd76c27e in exec_context_deserialize ../src/core/execute-serialize.c:3341
    #5 0x7f4efd778dcb in exec_deserialize ../src/core/execute-serialize.c:4122
    #6 0x4032c0 in LLVMFuzzerTestOneInput ../src/core/fuzz-execute-serialize.c:60
    #7 0x403c58 in main ../src/fuzz/fuzz-main.c:50
    #8 0x7f4efecccb49 in __libc_start_call_main (/lib64/libc.so.6+0x27b49) (BuildId: 245240a31888ad5c11bbc55b18e02d87388f59a9)
    #9 0x7f4efecccc0a in __libc_start_main_alias_2 (/lib64/libc.so.6+0x27c0a) (BuildId: 245240a31888ad5c11bbc55b18e02d87388f59a9)
    #10 0x402344 in _start (/home/mrc0mmand/repos/@systemd/systemd/build-san/fuzz-execute-serialize+0x402344) (BuildId: 195f382cf1e39b9ba48d6dcf5a90f786d72837a8)

SUMMARY: AddressSanitizer: 64 byte(s) leaked in 1 allocation(s).
Aborted (core dumped)

==911550==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 17 byte(s) in 1 object(s) allocated from:
    #0 0x4df281 in strdup (/home/mrc0mmand/repos/@systemd/systemd/build-libfuzz/fuzz-execute-serialize+0x4df281) (BuildId: 4e58706e607b8be7972d83c421bc0b625d509ec6)
    #1 0x7fe4ae2b38fc in _set_put_strndup_full /home/mrc0mmand/repos/@systemd/systemd/build-libfuzz/../src/basic/hashmap.c:1868:21
    #2 0x7fe4b0bad897 in exec_context_deserialize /home/mrc0mmand/repos/@systemd/systemd/build-libfuzz/../src/core/execute-serialize.c:3914:29
    #3 0x7fe4b0b80592 in exec_deserialize /home/mrc0mmand/repos/@systemd/systemd/build-libfuzz/../src/core/execute-serialize.c:4109:13
    #4 0x531d0f in LLVMFuzzerTestOneInput /home/mrc0mmand/repos/@systemd/systemd/build-libfuzz/../src/core/fuzz-execute-serialize.c:59:16
    #5 0x440594 in fuzzer::Fuzzer::ExecuteCallback(unsigned char const*, unsigned long) (/home/mrc0mmand/repos/@systemd/systemd/build-libfuzz/fuzz-execute-serialize+0x440594) (BuildId: 4e58706e607b8be7972d83c421bc0b625d509ec6)
    #6 0x43f9b9 in fuzzer::Fuzzer::RunOne(unsigned char const*, unsigned long, bool, fuzzer::InputInfo*, bool, bool*) (/home/mrc0mmand/repos/@systemd/systemd/build-libfuzz/fuzz-execute-serialize+0x43f9b9) (BuildId: 4e58706e607b8be7972d83c421bc0b625d509ec6)
    #7 0x440fd5 in fuzzer::Fuzzer::MutateAndTestOne() (/home/mrc0mmand/repos/@systemd/systemd/build-libfuzz/fuzz-execute-serialize+0x440fd5) (BuildId: 4e58706e607b8be7972d83c421bc0b625d509ec6)
    #8 0x441955 in fuzzer::Fuzzer::Loop(std::vector<fuzzer::SizedFile, std::allocator<fuzzer::SizedFile>>&) (/home/mrc0mmand/repos/@systemd/systemd/build-libfuzz/fuzz-execute-serialize+0x441955) (BuildId: 4e58706e607b8be7972d83c421bc0b625d509ec6)
    #9 0x42e151 in fuzzer::FuzzerDriver(int*, char***, int (*)(unsigned char const*, unsigned long)) (/home/mrc0mmand/repos/@systemd/systemd/build-libfuzz/fuzz-execute-serialize+0x42e151) (BuildId: 4e58706e607b8be7972d83c421bc0b625d509ec6)
    #10 0x45a916 in main (/home/mrc0mmand/repos/@systemd/systemd/build-libfuzz/fuzz-execute-serialize+0x45a916) (BuildId: 4e58706e607b8be7972d83c421bc0b625d509ec6)
    #11 0x7fe4ac449b49 in __libc_start_call_main (/lib64/libc.so.6+0x27b49) (BuildId: 245240a31888ad5c11bbc55b18e02d87388f59a9)
    #12 0x7fe4ac449c0a in __libc_start_main@GLIBC_2.2.5 (/lib64/libc.so.6+0x27c0a) (BuildId: 245240a31888ad5c11bbc55b18e02d87388f59a9)
    #13 0x422b74 in _start (/home/mrc0mmand/repos/@systemd/systemd/build-libfuzz/fuzz-execute-serialize+0x422b74) (BuildId: 4e58706e607b8be7972d83c421bc0b625d509ec6)
SUMMARY: AddressSanitizer: 17 byte(s) leaked in 1 allocation(s).

(cherry picked from commit 9b412709f21a4868e1bc0bb3252a4d26e862633b)
(cherry picked from commit 7bd680bc62c3d071ae6b4b4a834f79b4eceff0d8)
(cherry picked from commit b97ec522397d66d7df7c32f010f383e1e817c771)

src/core/cgroup.c

@@ -275,7 +275,7 @@ void cgroup_context_done(CGroupContext *c) {
         while (c->bpf_foreign_programs)
                 cgroup_context_remove_bpf_foreign_program(c, c->bpf_foreign_programs);
 
-        c->restrict_network_interfaces = set_free(c->restrict_network_interfaces);
+        c->restrict_network_interfaces = set_free_free(c->restrict_network_interfaces);
 
         cpu_set_reset(&c->cpuset_cpus);
         cpu_set_reset(&c->startup_cpuset_cpus);