ice: fix FDir IPv6 flexbyte

The packet classifier would occasionally misrecognize an IPv6 training
packet when the next protocol field was 0. The correct value for
unspecified protocol is IPPROTO_NONE.

Fixes: 165d80d6 ("ice: Support IPv6 Flow Director filters")
Signed-off-by: Henry Tieman <henry.w.tieman@intel.com>
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
Tested-by: Tony Brelinski <tonyx.brelinski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>