amd-xgbe: Check for complete packet on skb allocation error

If the skb allocation fails during receive processing, the driver would
continue reading descriptors without first determining if there were
any more descriptors for the current packet. Update the code to check
whether more descriptors are associated with the current packet or
whether to move on to the next descriptor as a new packet.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>