pfctl: allow include in inline anchors

with this,
anchor foo {

include "/path/to/rules"

}
works and "load anchor" is obsolete, to be removed somewhen later after
release.
co-production with reky at bsdcan, ok reyk mikeb benno sasha

Obtained from: OpenBSD, henning <henning@openbsd.org>, bf5a50acaa
Sponsored by: Rubicon Communications, LLC ("Netgate")