net: constify struct net_protocol

Remove long removed "inet_protocol_base" declaration.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index 97c410e..5bc13fe 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -655,7 +655,7 @@
 	struct iphdr *iph;
 	struct icmphdr *icmph;
 	int hash, protocol;
-	struct net_protocol *ipprot;
+	const struct net_protocol *ipprot;
 	u32 info = 0;
 	struct net *net;