e1000e: Correctly include VLAN_HLEN when changing interface MTU

e1000e: Correctly include VLAN_HLEN when changing interface MTU

When changing the interface mtu, the driver starts with a value
that doesn't include VLAN_HLEN.  Later tests in the driver
set the rx_buffer_len based on the mtu.  As a result, when
the user increases the mtu to 1504 (to support 802.1AD for example),
the driver rx_buffer_len does not change and frames longer
the 1522 bytes are rejected as too long.

Include VLAN_HLEN from the start so that an user mtu greater then
1500 bytes is correctly reflected in the driver rx_buffer_len.

CC: [email protected]
Signed-off-by: Vlad Yasevich <[email protected]>
Tested-by: Aaron Brown <[email protected]>
Signed-off-by: Jeff Kirsher <[email protected]>