net: bcmgenet: Add a check for oversized packets

[ Upstream commit 5c0862c2c962052ed5055220a00ac1cefb92fbcd ]

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.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>