NFSv4: Implement the fs_locations function call

NFSv4 allows for the fact that filesystems may be replicated across
several servers or that they may be migrated to a backup server in case of
failure of the primary server.
fs_locations is an NFSv4 operation for retrieving information about the
location of migrated and/or replicated filesystems.

Based on an initial implementation by Jiaying Zhang <jiayingz@citi.umich.edu>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

include/linux/nfs4.h

@@ -384,6 +384,7 @@ enum {
 	NFSPROC4_CLNT_DELEGRETURN,
 	NFSPROC4_CLNT_GETACL,
 	NFSPROC4_CLNT_SETACL,
+	NFSPROC4_CLNT_FS_LOCATIONS,
 };
 
 #endif