[Pal/Linux] Memorize the assigned ephemeral port during udp_bind()

In Linux, if a port number (in the input UDP socket address) during
`bind()` is specified as 0, an ephemeral (random) port is assigned.
Previously, Linux PAL forgot to update the port in the UDP socket
address, so `getsockname()` always returned 0 instead of the actual
port. This commit fixes this bug.

Signed-off-by: Sonali Saha <sonali.saha@intel.com>

LibOS/shim/test/ltp/ltp.cfg

@@ -1901,7 +1901,7 @@ timeout = 60
 [sendfile09_64]
 timeout = 60
 
-# EINVAL from native sendmsg()
+# uses recvmmsg(timeout) but timeout is unsupported in Gramine
 [sendmmsg01]
 skip = yes
 

Pal/src/host/Linux/db_sockets.c

@@ -609,6 +609,13 @@ static int udp_bind(PAL_HANDLE* handle, char* uri, int create, int options) {
         }
     }
 
+    /* call getsockname to get socket address */
+    ret = DO_SYSCALL(getsockname, fd, bind_addr, &bind_addrlen);
+    if (ret < 0) {
+        ret = unix_to_pal_error(ret);
+        goto failed;
+    }
+
     *handle = socket_create_handle(PAL_TYPE_UDPSRV, fd, options, bind_addr, bind_addrlen, NULL, 0);
 
     if (!(*handle)) {