net: bcmgenet: Add a check for oversized packets

In the Linux kernel, the following vulnerability has been resolved:

net: bcmgenet: Add a check for oversized packets

Occasionnaly we may get oversized packets from the hardware which exceed the nomimal 2KiB buffer size we allocate SKBs with. Add an early check which drops the packet to avoid invoking skb_over_panic() and move on to processing the next packet.