Use default memory type for TTM buffer objects that may be cached.

MFC after:	1 week


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273969 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
filedesc: move freeing old tables to fdescfree

They cannot be accessed by anyone and hold count only protects the structure
from being freed.


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273970 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f