igc: Make flex filter more flexible

Currently flex filters are only used for filters containing user data.
However, it makes sense to utilize them also for filters having
multiple conditions, because that's not supported by the driver at the
moment. Add it.

Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Tested-by: Dvora Fuxbrumer <dvorax.fuxbrumer@linux.intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>