Add RTEMS_BSD_CONFIG_xxx and rc.conf interface for PF

[Christian Mauderer]

The appended patch set adds

 - RTEMS_BSD_CONFIG_FIREWALL_PF
 - RTEMS_BSD_CONFIG_FIREWALL_PFLOG
 - RTEMS_BSD_CONFIG_FIREWALL_PFSYNC

for enabling the PF firewall. Further it adds an rc.conf interface that
mimics the one in FreeBSD. It handles the following directives:

 - pf_enable
 - pf_rules
 - pf_flags

It can't handle the pf_program directive.

Please note that I also increased the stack size of the rc-worker-task.
The task used far less stack than most of the testsuite and therefore
used an untested configuration.

Kind Regards

Christian Mauderer