vm: Fix racy checks for swap objects

Commit 4b8365d752ef introduced the ability to dynamically register
VM object types, for use by tmpfs, which creates swap-backed objects.
As a part of this, checks for such objects changed from

object->type == OBJT_DEFAULT || object->type == OBJT_SWAP

to

object->type == OBJT_DEFAULT || (object->flags & OBJ_SWAP) != 0

In particular, objects of type OBJT_DEFAULT do not have OBJ_SWAP set;
the swap pager sets this flag when converting from OBJT_DEFAULT to
OBJT_SWAP.

A few of these checks are done without the object lock held. It turns
out that this can result in false negatives since the swap pager
converts objects like so:

object->type = OBJT_SWAP;
object->flags |= OBJ_SWAP;

Fix the problem by adding explicit tests for OBJT_SWAP objects in
unlocked checks.

PR: 258932
Fixes: 4b8365d752ef ("Add OBJT_SWAP_TMPFS pager")
Reported by: bdrewery
Reviewed by: kib
MFC after: 2 weeks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D35470