cxgb4: fix extracting IP addresses in TC-FLOWER rules

commit c8729cac ("cxgb4: add ethtool n-tuple filter insertion")
has removed checking control key for determining IP address types
for TC-FLOWER rules, which causes all the rules being inserted to
hardware to become IPv6 rule type always. So, add back the check
to select the correct IP address type to extract and hence fix the
correct rule type being inserted to hardware.

Also, ethtool_rx_flow_key doesn't have any control key and instead
directly sets the IPv4/IPv6 address keys. So, explicitly set the
IP address type for ethtool n-tuple filters to reuse the same code.

Fixes: c8729cac ("cxgb4: add ethtool n-tuple filter insertion")
Signed-off-by: Rahul Lakkireddy <rahul.lakkireddy@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>