net: Fix build failures due to ip_is_fragment()

It needs to be available even when CONFIG_INET is not set.
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Reported-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/ip.h

@@ -236,6 +236,11 @@ extern void ipfrag_init(void);
 
 extern void ip_static_sysctl_init(void);
 
+static inline bool ip_is_fragment(const struct iphdr *iph)
+{
+	return (iph->frag_off & htons(IP_MF | IP_OFFSET)) != 0;
+}
+
 #ifdef CONFIG_INET
 #include <net/dst.h>
 
@@ -250,11 +255,6 @@ int ip_decrease_ttl(struct iphdr *iph)
 	return --iph->ttl;
 }
 
-static inline bool ip_is_fragment(const struct iphdr *iph)
-{
-	return (iph->frag_off & htons(IP_MF | IP_OFFSET)) != 0;
-}
-
 static inline
 int ip_dont_fragment(struct sock *sk, struct dst_entry *dst)
 {