route: remove write-only struct hostent from getaddr()

Under some INET/INET6 src.conf configurations sbin/route previously
failed to build due to an unused variable warning. It was functionally
write-only anyway, so just remove it.

Reported by: melifaro
Reviewed by: melifaro
MFC after: 3 weeks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D33717

(cherry picked from commit c2173903598a33122a8006a944158b95dd5e2d80)
(cherry picked from commit f567fcb2ffc4180319e644796d6dbc51b51a4e04)