net, thunderx: Remove unnecessary rcv buffer start address management

Since we have moved on to using allocated pages to carve receive
buffers instead of netdev_alloc_skb() there is no need to store
any pointers for later retrieval. Earlier we had to store
skb and skb->data pointers which later are used to handover
received packet to network stack.

This will avoid an unnecessary cache miss as well.

Signed-off-by: Sunil Goutham <sgoutham@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>