Fix key lookup in ipfw(8) broken since r232865.
Print warning for IPv4 address strings which are valid in
inet_aton() but not valid in inet_pton(). (1)

Found by:	Özkan KIRIK <ozkan.kirik@gmail.com>
Submitted by:	Ian Smith <smithi@nimnet.asn.au> (1)
MFC after:	2 weeks
Sponsored by:	Yandex LLC