nfsd4: fix v3-less build

Includes of pnfs.h in export.c and fcntl.c also bring in xdr4.h, which
won't build without CONFIG_NFSD_V3, breaking non-V3 builds. Ifdef-out
most of pnfs.h in that case.

Reported-by: Bas Peters <[e-mail]>
Reported-by: Jim Davis <[e-mail]>
Tested-by: Guenter Roeck <[e-mail]>
Fixes: 9cf514ccfac "nfsd: implement pNFS operations"
Signed-off-by: J. Bruce Fields <[e-mail]>

fs/nfsd/pnfs.h

···
 #ifndef _FS_NFSD_PNFS_H
 #define _FS_NFSD_PNFS_H 1
 
+#ifdef CONFIG_NFSD_V4
 #include <linux/exportfs.h>
 #include <linux/nfsd/export.h>
 
···
 int nfsd4_set_deviceid(struct nfsd4_deviceid *id, const struct svc_fh *fhp,
 		u32 device_generation);
 struct nfsd4_deviceid_map *nfsd4_find_devid_map(int idx);
+#endif /* CONFIG_NFSD_V4 */
 
 #ifdef CONFIG_NFSD_PNFS
 void nfsd4_setup_layout_type(struct svc_export *exp);
···
 int nfsd4_init_pnfs(void);
 void nfsd4_exit_pnfs(void);
 #else
+struct nfs4_client;
+struct nfs4_file;
+
 static inline void nfsd4_setup_layout_type(struct svc_export *exp)
 {
 }