igb: move the tx and rx ring specific config into seperate functions

This change makes the tx and rx config a bit cleaner by breaking out the ring
specific configuration from the generic rx and tx configuration.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>