e1000e: low throughput using 4K jumbos on I218

Alter the packet buffer allocation accordingly.
Signed-off-by: NBruce Allan <bruce.w.allan@intel.com>
Tested-by: NJeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/e1000e/netdev.c

@@ -3819,6 +3819,8 @@ void e1000e_reset(struct e1000_adapter *adapter)
 			break;
 		}
 
+		pba = 14;
+		ew32(PBA, pba);
 		fc->high_water = ((pba << 10) * 9 / 10) & E1000_FCRTH_RTH;
 		fc->low_water = ((pba << 10) * 8 / 10) & E1000_FCRTL_RTL;
 		break;