sysutils/pftop: Update to 0.9 (support 15-CURRENT)

All local patches have been upstreamed and upstream has been cleaned up
by removing support for outdated versions of FreeBSD.

The tool now depends on net/libpfctl, important work contributed
by kp@, which means that pftop will now work on 15-CURRENT
and its code could be simplified due to having an abstraction
for supporting multiple releases of FreeBSD.