Log Message:
sysutils/pftop: support newer PF and depend on osabi

* In order for pftop to be built successfully with newer PF
versions (> 4.1), additional patches are necessary which were taken
from OpenBSD's ports as seen in PR pkg/44339
* Pftop compiled for another PF version will not work (properly),
so to avoid any problems we must depend on the OS version

ok@ wiz