igc: add support to set tx-min-frag-size

Add support for setting tx-min-frag-size via the set_mm callback in igc.
If the requested value is unsupported, round it up to the smallest
supported i226 size (64, 128, 192, 256) and send a netlink message to
inform the user.

Co-developed-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Faizal Rahim <faizal.abdul.rahim@linux.intel.com>
Tested-by: Mor Bar-Gabay <morx.bar.gabay@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>