new helpers: fh_{want,drop}_write()

A bunch of places in nfsd does mnt_{want,drop}_write on vfsmount of
export of given fhandle.  Switched to obvious inlined helpers...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/nfsd/vfs.h b/fs/nfsd/vfs.h
index 3f54ad0..cee6a12 100644
--- a/fs/nfsd/vfs.h
+++ b/fs/nfsd/vfs.h
@@ -106,4 +106,14 @@
 int nfsd_set_posix_acl(struct svc_fh *, int, struct posix_acl *);
 #endif
 
+static inline int fh_want_write(struct svc_fh *fh)
+{
+	return mnt_want_write(fh->fh_export->ex_path.mnt);
+}
+
+static inline void fh_drop_write(struct svc_fh *fh)
+{
+	mnt_drop_write(fh->fh_export->ex_path.mnt);
+}
+
 #endif /* LINUX_NFSD_VFS_H */