ofproto: make oftable_remove_rule__ release evict lock

ofproto: make oftable_remove_rule__ release evict lock

according to the OVS_RELEASES annotation, oftable_remove_rule__ is
expected to release rule->evict lock.  make it actually do so.

this fixes pthread_rwlock_destroy failures observed on NetBSD,
where destroying a held lock, which is specwise undefined behaviour,
actually fails.  i guess it doesn't fail on linux but it's better
not to rely on an undefined behavior.

Signed-off-by: YAMAMOTO Takashi <yamt@mwd.biglobe.ne.jp>
Signed-off-by: Ben Pfaff <blp@nicira.com>