skmsg: Fix a memory leak in sk_psock_verdict_apply()

If the dest psock does not set SK_PSOCK_TX_ENABLED,
the skb can't be queued anywhere so must be dropped.

This one is found during code review.

Fixes: 799aa7f9 ("skmsg: Avoid lock_sock() in sk_psock_backlog()")
Signed-off-by: Cong Wang <cong.wang@bytedance.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Jakub Sitnicki <jakub@cloudflare.com>
Link: https://lore.kernel.org/bpf/20210615021342.7416-6-xiyou.wangcong@gmail.com