e1000e: packet split should not be used with early receive

Originally it was thought there were issues with ICHx/PCH parts with packet
split when jumbo frames were enabled but in fact it is really only when
early-receive is enabled (via ERT register) on these parts.  Use packet
split with jumbos but only when early-receive is not enabled.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>