ipv4: avoid passing NULL to inet_putpeer() in icmpv4_xrlim_allow()

inet_getpeer_v4() can return NULL under OOM conditions, and while
inet_peer_xrlim_allow() is OK with a NULL peer, inet_putpeer() will
crash.

This code path now uses the same idiom as the others from:
1d861aa4 ("inet: Minimize use of
cached route inetpeer.").
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/icmp.c

@@ -257,7 +257,8 @@ static inline bool icmpv4_xrlim_allow(struct net *net, struct rtable *rt,
 		struct inet_peer *peer = inet_getpeer_v4(net->ipv4.peers, fl4->daddr, 1);
 		rc = inet_peer_xrlim_allow(peer,
 					   net->ipv4.sysctl_icmp_ratelimit);
-		inet_putpeer(peer);
+		if (peer)
+			inet_putpeer(peer);
 	}
 out:
 	return rc;