selftests/bpf: Fix memory leak in msg_alloc_iov error path

In msg_alloc_iov(), when calloc() fails for an individual iov_base
allocation, the error path frees all previously allocated iov_base
entries but fails to free the iov array itself that was allocated
with calloc() at the beginning of the function. This results in a
memory leak of the iov array.

Add free(iov) in the unwind_iov error path to ensure proper cleanup
of all allocated memory.

Fixes: 753fb2ee09 ("bpf: sockmap, add msg_peek tests to test_sockmap")
Signed-off-by: Malaya Kumar Rout <malayarout91@gmail.com>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Link: https://lore.kernel.org/bpf/20260704122936.102394-1-malayarout91@gmail.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

tools/testing/selftests/bpf/test_sockmap.c

@@ -436,6 +436,7 @@ static int msg_alloc_iov(struct msghdr *msg,
 unwind_iov:
 	for (i--; i >= 0 ; i--)
 		free(msg->msg_iov[i].iov_base);
+	free(iov);
 	return -ENOMEM;
 }