pf: fix build on kernels without "options INET"

• IN_LOOPBACK() cannot be used without INET, because it references a VNET symbol vnet_entry_in_loopback_mask.

• ip_fillid() is not available without INET. since this codepath is only entered in the AF_INET case, guard it with #ifnet INET.

Fixes: 27f54be50bbad ("pf: merge pf_test() and pf_test6()")
Fixes: 4f9e688708f1b ("pf: merge pf_scrub_ip() and pf_scrub_ip6()")
Reviewed by: kp