drivers: net: xgene: Refactor statistics error parsing code

This patch fixes the tx error counters and adds more rx error counters.

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