linux-phytec-ti

net: hsr/prp: expand MTU size by 6 when offloaded

With hsr or prp devices that are offloaded Ethernet devices, expand
MTU size to 1500 (ETH_DATA_LEN) as these devices can set the Max
frame length to 1528 with VLAN + Tag/RCT. So keep the MTU size at 1500
when offloaded and doesn't include tag/rct as part of the payload as
is done currently. The assumption is offloaded devices must expand the
frame size to accommodate the extra 6 bytes of Tag/RCT.

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>