pf: fix anchor quick with nested anchors

We lost the quick flag as soon as we stepped into a child anchor.
Simplify the logic, get rid of the match flag in the anchor stack, just
use the match variable we already had (and used in a boolean style) to track
the nest level we had a match at. When a child anchor had a match we also
have a match in the current anchor, so update the match level accordingly,
and thus correctly honour the quick flag.
Reported by, along with the right idea on how to fix this, by Sean Gallagher
\sean at teletech.com.au/, who also helped testing the fix. ok ryan & benno

Obtained from: OpenBSD, henning <henning@openbsd.org>, 32a028bff7
Sponsored by: Rubicon Communications, LLC ("Netgate")