nfs_xdr: Move nfs4_string definition out of #ifdef CONFIG_NFS_V4

exofs file system wants to use pnfs_osd_xdr.h file instead of
redefining pnfs-objects types in it's private "pnfs.h" headr.

Before we do the switch we must make sure pnfs_osd_xdr.h is
compilable also under NFS versions smaller than 4.1. Since now
it is needed regardless of version, by the exofs code.

nfs4_string is not the only nfs4 type out in the global scope.
Ack-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>

include/linux/nfs_xdr.h

@@ -759,6 +759,11 @@ struct nfs3_getaclres {
 	struct posix_acl *	acl_default;
 };
 
+struct nfs4_string {
+	unsigned int len;
+	char *data;
+};
+
 #ifdef CONFIG_NFS_V4
 
 typedef u64 clientid4;
@@ -949,11 +954,6 @@ struct nfs4_server_caps_res {
 	struct nfs4_sequence_res	seq_res;
 };
 
-struct nfs4_string {
-	unsigned int len;
-	char *data;
-};
-
 #define NFS4_PATHNAME_MAXCOMPONENTS 512
 struct nfs4_pathname {
 	unsigned int ncomponents;