e1000e: specify max supported frame size in adapter struct

By putting the maximum frame size supported by the hardware into the
adapter structure, the change_mtu entry point function can be cleaned
up of checks for all the different max frame sizes supported by

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/e1000e/es2lan.c b/drivers/net/e1000e/es2lan.c
index 8964838..6cc3bdf 100644
--- a/drivers/net/e1000e/es2lan.c
+++ b/drivers/net/e1000e/es2lan.c
@@ -1422,6 +1422,7 @@
 				  | FLAG_DISABLE_FC_PAUSE_TIME /* errata */
 				  | FLAG_TIPG_MEDIUM_FOR_80003ESLAN,
 	.pba			= 38,
+	.max_hw_frame_size	= DEFAULT_JUMBO,
 	.get_variants		= e1000_get_variants_80003es2lan,
 	.mac_ops		= &es2_mac_ops,
 	.phy_ops		= &es2_phy_ops,