Always pass MNT_NOWAIT to getfsstat() as documented in the manpage.

One of the four calls in net-snmp currently passes 0 which triggers an
EINVAL change after recent changes in HEAD and 11-stable to add stricter
argument checking for the flags passed to getsstat().

Bump PORTREVISION.

PR: 218011
Reported by: Slawa Olhovchenkov <slw@zxy.spb.ru>
Reviewed by: brooks
Approved by: maintainer (zi)