vsock/test: Add test for sk_error_queue memory leak

Ask for MSG_ZEROCOPY completion notification, but do not recv() it.
Test attempts to create a memory leak, kmemleak should be employed.

Fixed by commit fbf7085b ("vsock: Fix sk_error_queue memory leak").

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Link: https://patch.msgid.link/20241219-test-vsock-leaks-v4-6-a416e554d9d7@rbox.co


Signed-off-by: Jakub Kicinski <kuba@kernel.org>