MFC r341326

MFC r341326

sfxge(4): ensure EvQ poll stops when abort is requested

If an event handler requested an abort, only the inner loop was
guarenteed to be broken out of - the outer loop could continue
if total == batch.

Fix this by poisoning batch to ensure it is different to total.

Submitted by:   Mark Spender <mspender at solarflare.com>
Sponsored by:   Solarflare Communications, Inc.
Differential Revision:  https://reviews.freebsd.org/D18287

git-svn-id: svn://svn.freebsd.org/base/stable/10@342521 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f