igmp: uninline ip_mc_validate_checksum()

This function is only used via function pointer.

"inline" doesn't hurt given that taking address of an inline function
forces out-of-line version but it doesn't help either.
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/igmp.c

@@ -1563,7 +1563,7 @@ static int ip_mc_check_igmp_msg(struct sk_buff *skb)
 	}
 }
 
-static inline __sum16 ip_mc_validate_checksum(struct sk_buff *skb)
+static __sum16 ip_mc_validate_checksum(struct sk_buff *skb)
 {
 	return skb_checksum_simple_validate(skb);
 }