crypto: af_alg - Use bh_lock_sock in sk_destruct

As af_alg_release_parent may be called from BH context (most notably
due to an async request that only completes after socket closure,
or as reported here because of an RCU-delayed sk_destruct call), we
must use bh_lock_sock instead of lock_sock.

Reported-by:  <syzbot+c2f1558d49e25cc36e5e@syzkaller.appspotmail.com>
Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
Fixes: c840ac6a

 ("crypto: af_alg - Disallow bind/setkey/...")
Cc: <stable@vger.kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>