Remove the thread argument from the FSD (File-System Dependent) parts of

the VFS.  Now all the VFS_* functions and relating parts don't want the
context as long as it always refers to curthread.

In some points, in particular when dealing with VOPs and functions living
in the same namespace (eg. vflush) which still need to be converted,
pass curthread explicitly in order to retain the old behaviour.
Such loose ends will be fixed ASAP.

While here fix a bug: now, UFS_EXTATTR can be compiled alone without the
UFS_EXTATTR_AUTOSTART option.

VFS KPI is heavilly changed by this commit so thirdy parts modules needs
to be recompiled.  Bump __FreeBSD_version in order to signal such
situation.

sys/kern/uipc_mqueue.c

@@ -561,7 +561,7 @@ mqfs_destroy(struct mqfs_node *node)
  * Mount a mqfs instance
  */
 static int
-mqfs_mount(struct mount *mp, struct thread *td)
+mqfs_mount(struct mount *mp)
 {
 	struct statfs *sbp;
 
@@ -591,11 +591,12 @@ mqfs_mount(struct mount *mp, struct thread *td)
  * Unmount a mqfs instance
  */
 static int
-mqfs_unmount(struct mount *mp, int mntflags, struct thread *td)
+mqfs_unmount(struct mount *mp, int mntflags)
 {
 	int error;
 
-	error = vflush(mp, 0, (mntflags & MNT_FORCE) ?  FORCECLOSE : 0, td);
+	error = vflush(mp, 0, (mntflags & MNT_FORCE) ?  FORCECLOSE : 0,
+	    curthread);
 	return (error);
 }
 
@@ -603,7 +604,7 @@ mqfs_unmount(struct mount *mp, int mntflags, struct thread *td)
  * Return a root vnode
  */
 static int
-mqfs_root(struct mount *mp, int flags, struct vnode **vpp, struct thread *td)
+mqfs_root(struct mount *mp, int flags, struct vnode **vpp)
 {
 	struct mqfs_info *mqfs;
 	int ret;
@@ -617,7 +618,7 @@ mqfs_root(struct mount *mp, int flags, struct vnode **vpp, struct thread *td)
  * Return filesystem stats
  */
 static int
-mqfs_statfs(struct mount *mp, struct statfs *sbp, struct thread *td)
+mqfs_statfs(struct mount *mp, struct statfs *sbp)
 {
 	/* XXX update statistics */
 	return (0);