net_device: Avoid unnecessary checksum calculation
net_device: Avoid unnecessary checksum calculation

Checksum was being calculated in a case where this is not necessary.
Specifically when checksum offload is disabled and so is MRG_RXBUF.

eugeneia/snabbswitch,snabbco/snabb,Igalia/snabb,eugeneia/snabb,snabbco/snabb,eugeneia/snabb,Igalia/snabbswitch,alexandergall/snabbswitch,alexandergall/snabbswitch,wingo/snabb,dpino/snabb,wingo/snabbswitch,Igalia/snabb,snabbco/snabb,heryii/snabb,alexandergall/snabbswitch,mixflowtech/logsensor,eugeneia/snabb,dpino/snabbswitch,heryii/snabb,mixflowtech/logsensor,Igalia/snabbswitch,eugeneia/snabbswitch,heryii/snabb,kbara/snabb,Igalia/snabb,snabbco/snabb,heryii/snabb,Igalia/snabb,eugeneia/snabb,snabbco/snabb,dpino/snabbswitch,Igalia/snabbswitch,dpino/snabb,kbara/snabb,heryii/snabb,dpino/snabb,wingo/snabbswitch,dpino/snabb,eugeneia/snabb,alexandergall/snabbswitch,eugeneia/snabbswitch,mixflowtech/logsensor,SnabbCo/snabbswitch,kbara/snabb,wingo/snabb,eugeneia/snabb,dpino/snabb,snabbco/snabb,Igalia/snabbswitch,alexandergall/snabbswitch,kbara/snabb,Igalia/snabb,SnabbCo/snabbswitch,wingo/snabb,dpino/snabbswitch,alexandergall/snabbswitch,mixflowtech/logsensor,SnabbCo/snabbswitch,mixflowtech/logsensor,alexandergall/snabbswitch,Igalia/snabb,Igalia/snabb,snabbco/snabb,dpino/snabb,kbara/snabb,wingo/snabbswitch,dpino/snabbswitch,Igalia/snabb,eugeneia/snabb,Igalia/snabbswitch,wingo/snabb,dpino/snabb,alexandergall/snabbswitch,eugeneia/snabb,wingo/snabb,wingo/snabbswitch,SnabbCo/snabbswitch,eugeneia/snabbswitch,snabbco/snabb,heryii/snabb,kbara/snabb,wingo/snabb