pfsync: Allow module to be unloaded

[glebius]

I'm not absolutely sure that all possible races are fixed. There still could be dangling ifnet pointers. But that's up to your justification. If you are sure everything is covered, feel free to remove.

As for me personally, I'm fine to type 'kldunload -f' when I do kernel hacking. A normal sysadmin shouldn't need to unload the module. If they really need (why?) then 'kldunload -f' is always available.

[kp]

In D17505#379676, @glebius wrote:

I'm not absolutely sure that all possible races are fixed. There still could be dangling ifnet pointers. But that's up to your justification. If you are sure everything is covered, feel free to remove.

I'm not currently aware of any remaining issues here. It's certainly possible that some still exist, but I've seen no reports and the tests don't provoke them.
I think of this change mostly as a 'I will support this now.' statement.