pfsync: Expose PFSYNCF_OK flag to userspace

[kp]

Summary

Add 'syncok' field to ifconfig's pfsync interface output. This allows
userspace to figure out when pfsync has completed the initial bulk
import.

MFC after: 2 weeks
Sponsored by: Rubicon Communications, LLC ("Netgate")

[donner]

sbin/ifconfig/ifpfsync.c

209–213

How about "defer: on (loaded)" in order to keep the line count.

[kp]

sbin/ifconfig/ifpfsync.c

209–213

I initially considered adding it as 'syncok: 1' behind the 'defer: ...' line, but kept it on its own line to avoid breaking ifconfig parsers.
The same objection applies to '(loaded)'.

Sadly we don't yet have libxo support in ifconfig, so people tend to grep/awk/sed/... the ifconfig output, and if we add a line we're much less likely to break those parsers than if we add something to an existing output line.