The OBJ_TMPFS flag of vm_object means that there is unreclaimed tmpfs
vnode for the tmpfs node owning this object.  The flag is currently
used for two purposes.  First, it allows to correctly handle VV_TEXT
for tmpfs vnode when the ref count on the object is decremented to 1,
similar to vnode_pager_dealloc() for regular filesystems.  Second, it
prevents some operations, which are done on OBJT_SWAP vm objects
backing user anonymous memory, but are incorrect for the object owned
by tmpfs node.

The second kind of use of the OBJ_TMPFS flag is incorrect, since the
vnode might be reclaimed, which clears the flag, but vm object
operations must still be disallowed.

Introduce one more flag, OBJ_TMPFS_NODE, which is permanently set on
the object for VREG tmpfs node, and used instead of OBJ_TMPFS to test
whether vm object collapse and similar actions should be disabled.

Tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks
Change forgotten in r268615.  Set the OBJ_TMPFS_NODE flag for
vm_object of VREG tmpfs node.

Tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks