bpf: add initial suite for selftests

Add a start of a test suite for kernel selftests. This moves test_verifier
and test_maps over to tools/testing/selftests/bpf/ along with various
code improvements and also adds a script for invoking test_bpf module.
The test suite can simply be run via selftest framework, f.e.:

  # cd tools/testing/selftests/bpf/
  # make
  # make run_tests

Both test_verifier and test_maps were kind of misplaced in samples/bpf/
directory and we were looking into adding them to selftests for a while
now, so it can be picked up by kbuild bot et al and hopefully also get
more exposure and thus new test case additions.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

MAINTAINERS

@@ -2521,6 +2521,8 @@ L:	netdev@vger.kernel.org
 L:	linux-kernel@vger.kernel.org
 S:	Supported
 F:	kernel/bpf/
+F:	tools/testing/selftests/bpf/
+F:	lib/test_bpf.c
 
 BROADCOM B44 10/100 ETHERNET DRIVER
 M:	Michael Chan <michael.chan@broadcom.com>
@@ -8413,7 +8415,6 @@ F:	include/uapi/linux/net_namespace.h
 F:	tools/net/
 F:	tools/testing/selftests/net/
 F:	lib/random32.c
-F:	lib/test_bpf.c
 
 NETWORKING [IPv4/IPv6]
 M:	"David S. Miller" <davem@davemloft.net>

samples/bpf/Makefile

@@ -2,7 +2,6 @@
 obj- := dummy.o
 
 # List of programs to build
-hostprogs-y := test_verifier test_maps
 hostprogs-y += sock_example
 hostprogs-y += fds_example
 hostprogs-y += sockex1
@@ -28,8 +27,6 @@ hostprogs-y += test_current_task_under_cgroup
 hostprogs-y += trace_event
 hostprogs-y += sampleip
 
-test_verifier-objs := test_verifier.o libbpf.o
-test_maps-objs := test_maps.o libbpf.o
 sock_example-objs := sock_example.o libbpf.o
 fds_example-objs := bpf_load.o libbpf.o fds_example.o
 sockex1-objs := bpf_load.o libbpf.o sockex1_user.o