NFSD: Include <linux/nfs_fh.h> where struct nfs_fh is used

struct nfsd4_copy embeds a struct nfs_fh, and nlm_fopen() reads the
size and data fields of one. Neither fs/nfsd/xdr4.h nor
fs/nfsd/lockd.c includes the header that defines the type; both
reach it by way of nfsd.h, which pulls in <linux/nfs.h>.

Add the direct include to both files, so nfsd.h can later drop the
<linux/nfs.h> it carries for no use of its own.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260818140035.12740-2-cel@kernel.org
Signed-off-by: Chuck Lever <cel@kernel.org>

fs/nfsd/lockd.c

@@ -9,6 +9,7 @@
 
 #include <linux/file.h>
 #include <linux/lockd/bind.h>
+#include <linux/nfs_fh.h>
 #include "nfsd.h"
 #include "nfserr.h"
 #include "vfs.h"

fs/nfsd/xdr4.h

@@ -37,6 +37,8 @@
 #ifndef _LINUX_NFSD_XDR4_H
 #define _LINUX_NFSD_XDR4_H
 
+#include <linux/nfs_fh.h>
+
 #include "state.h"
 #include "vfs.h"