net/libpfctl: add 15.2, remove 15.0
15.0 is end-of-life, remove it from this port.
Add 15.2, which is in the process of being released.
Deliberately do not bump PORTVERSION, because we don't change existing
libpfctl versions, we only add a new supported FreeBSD version.
PR: 300134
Sponsored by: Rubicon Communications, LLC ("Netgate")