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