tcp: use 2-arg optimal variant of kfree_rcu()

kfree_rcu(1-arg) should be avoided as much as possible,
since this is only possible from sleepable contexts,
and incurr extra rcu barriers.

I wish the 1-arg variant of kfree_rcu() would
get a distinct name, like kfree_rcu_slow()
to avoid it being abused.

Fixes: 459837b ("net/tcp: Disable TCP-MD5 static key on tcp_md5sig_info destruction")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Reviewed-by: Dmitry Safonov <dima@arista.com>
Link: https://lore.kernel.org/r/20221202052847.2623997-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/tcp_ipv4.c

@@ -1245,7 +1245,7 @@ int tcp_md5_do_add(struct sock *sk, const union tcp_md5_addr *addr,
 
 			md5sig = rcu_dereference_protected(tp->md5sig_info, lockdep_sock_is_held(sk));
 			rcu_assign_pointer(tp->md5sig_info, NULL);
-			kfree_rcu(md5sig);
+			kfree_rcu(md5sig, rcu);
 			return -EUSERS;
 		}
 	}
@@ -1271,7 +1271,7 @@ int tcp_md5_key_copy(struct sock *sk, const union tcp_md5_addr *addr,
 			md5sig = rcu_dereference_protected(tp->md5sig_info, lockdep_sock_is_held(sk));
 			net_warn_ratelimited("Too many TCP-MD5 keys in the system\n");
 			rcu_assign_pointer(tp->md5sig_info, NULL);
-			kfree_rcu(md5sig);
+			kfree_rcu(md5sig, rcu);
 			return -EUSERS;
 		}
 	}