[UDP]: Move udp_stats_in6 into net/ipv4/udp.c

Now that external users may increment the counters directly, we need
to ensure that udp_stats_in6 is always available.  Otherwise we'd
either have to requrie the external users to be built as modules or
ipv6 to be built-in.

This isn't too bad because udp_stats_in6 is just a pair of pointers
plus an EXPORT, e.g., just 40 (16 + 24) bytes on x86-64.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/udp.c

@@ -112,6 +112,9 @@
 DEFINE_SNMP_STAT(struct udp_mib, udp_statistics) __read_mostly;
 EXPORT_SYMBOL(udp_statistics);
 
+DEFINE_SNMP_STAT(struct udp_mib, udp_stats_in6) __read_mostly;
+EXPORT_SYMBOL(udp_stats_in6);
+
 struct hlist_head udp_hash[UDP_HTABLE_SIZE];
 DEFINE_RWLOCK(udp_hash_lock);
 

net/ipv6/udp.c

@@ -51,9 +51,6 @@
 #include <linux/seq_file.h>
 #include "udp_impl.h"
 
-DEFINE_SNMP_STAT(struct udp_mib, udp_stats_in6) __read_mostly;
-EXPORT_SYMBOL(udp_stats_in6);
-
 static inline int udp_v6_get_port(struct sock *sk, unsigned short snum)
 {
 	return udp_get_port(sk, snum, ipv6_rcv_saddr_equal);