The recent change to DIOCGETRULE allows applications which

The recent change to DIOCGETRULE allows applications which
periodically read rules from pf(4) to consume all kernel
memory. The bug has been discovered and root caused by florian@.
In this particular case it was snmpd(8) what ate all kernel
memory.

This commit introduces DIOCXEND to pf(4) so applications such
as snmpd(8) and systat(1) to close ticket/transaction when
they are done with fetching the rules. This change also
updates snmpd(8) and systat(1) to use newly introduced
DIOCXEND ioctl(2).

OK claudio@, deraadt@, kn@