ping: remove pr_err from ping_lookup

As Jakub noticed, prints should be avoided on the datapath.
Also, as packets would never come to the else branch in
ping_lookup(), remove pr_err() from ping_lookup().

Fixes: 35a79e6 ("ping: fix the dif and sdif check in ping_lookup")
Reported-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Link: https://lore.kernel.org/r/1ef3f2fcd31bd681a193b1fcf235eee1603819bd.1645674068.git.lucien.xin@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/ping.c

@@ -187,7 +187,6 @@ static struct sock *ping_lookup(struct net *net, struct sk_buff *skb, u16 ident)
 			 (int)ident, &ipv6_hdr(skb)->daddr, dif);
 #endif
 	} else {
-		pr_err("ping: protocol(%x) is not supported\n", ntohs(skb->protocol));
 		return NULL;
 	}