MFstable/10 r289949:

MFstable/10 r289949:

MFC r286304:

Set f_file to -1/F_UNUSED when after closing when possible

This will help ensure we don't trash file descriptors that get used later on
in the daemon

Found via internal Coverity scan

Discussed with: cem, ed, markj
Differential Revision: https://reviews.freebsd.org/D3081
Submitted by: Miles Ohlrich <miles.ohlrich@isilon.com>
Sponsored by: EMC / Isilon Storage Division

git-svn-id: svn://svn.freebsd.org/base/stable/9@289950 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f