ice: breakout common LAG code into helpers

In the VF handling code, parts of the code for lag can be broken out into
helper functions to reduce code duplication. Break this code out into
helper functions

Reviewed-by: Marcin Szycik <marcin.szycik@linux.intel.com>
Signed-off-by: Dave Ertman <david.m.ertman@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>