vfs: don't recycle transiently excess vnodes

Sponsored by: Rubicon Communications, LLC ("Netgate")

(cherry picked from commit a4f753e812d8913e9be481c6dfa1574c7f032a56)
(cherry picked from commit e3b2372a76c18551529e1aa43d185f602dccdbf1)

Approved by: re (gjb)