IPv6 support for NFS server export caches

This adds IPv6 support to the interfaces that are used to express nfsd
exports.  All addressed are stored internally as IPv6; backwards
compatibility is maintained using mapped addresses.

Thanks to Bruce Fields, Brian Haley, Neil Brown and Hideaki Joshifuji
for comments

Signed-off-by: Aurelien Charbon <aurelien.charbon@bull.net>
Cc: Neil Brown <neilb@suse.de>
Cc: Brian Haley <brian.haley@hp.com>
Cc:  YOSHIFUJI Hideaki / 吉藤英明 <yoshfuji@linux-ipv6.org>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
diff --git a/include/net/ipv6.h b/include/net/ipv6.h
index 49c4898..e0a612b 100644
--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -383,6 +383,15 @@
 		== htonl(0x20010010));
 }
 
+static inline void ipv6_addr_set_v4mapped(const __be32 addr,
+					  struct in6_addr *v4mapped)
+{
+	ipv6_addr_set(v4mapped,
+			0, 0,
+			htonl(0x0000FFFF),
+			addr);
+}
+
 /*
  * find the first different bit between two addresses
  * length of address must be a multiple of 32bits