cxgb4: fix regression with HASH tc prio value update

commit db43b30c ("cxgb4: add ethtool n-tuple filter deletion")
has moved searching for next highest priority HASH filter rule to
cxgb4_flow_rule_destroy(), which searches the rhashtable before the
the rule is removed from it and hence always finds at least 1 entry.
Fix by removing the rule from rhashtable first before calling
cxgb4_flow_rule_destroy() and hence avoid fetching stale info.

Fixes: db43b30c

 ("cxgb4: add ethtool n-tuple filter deletion")
Signed-off-by: Rahul Lakkireddy <rahul.lakkireddy@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>