drivers: net: xgene: Add support for Jumbo frame

This patch adds support for jumbo frame, by allocating
additional buffer (page) pool and configuring the hardware.

Signed-off-by: Iyappan Subramanian <isubramanian@apm.com>
Signed-off-by: Quan Nguyen <qnguyen@apm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>