ipvs: Fix race conditions in lblcr scheduler

We can't access the cache entry outside of our critical read-locked region,
because someone may free that entry. Also getting an entry under read lock,
then locking for write and trying to delete that entry looks fishy, but should
be no problem here, because we're only comparing a pointer. Also there is no
need for our own rwlock, there is already one in the service structure for use
in the schedulers.

Signed-off-by: Sven Wegener <sven.wegener@stealer.net>
Signed-off-by: Simon Horman <horms@verge.net.au>