lib/route-table-*: Fix non-Linux builds

Fix build failures introduced by
commit 1bc50ef389d40be9ee215e66b49cf66fcbdb9eeb
("dpctl: Fix crash.")

Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Acked-by: Ben Pfaff <blp@nicira.com>