pfsync: Unconditionally push packets when requesting state updates

When we request a bulk sync we need to ensure we actually send out that
request, not just buffer it until we have enough data to send a full
packet.

PR: 254236
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D29271

(cherry picked from commit 9f2e5184173f6af70306678b018270df9a9600f2)