Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

libpfct: Fix PIC flag

Use ${PICFLAG} rather than hard-adding -fPIC, which removes the
requirement for libnv to be built PIC.

MFC after: 4 weeks
Sponsored by: Rubicon Communications, LLC ("Netgate")

pfctl: Move ioctl abstraction functions into libpfctl

Introduce a library to wrap the pf ioctl interface.

MFC after: 4 weeks
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D29562