One to notify the system that the MTU for VLAN can be 1500 so the vlan
will automatically be configured with a 1500 MTU the other is to ignore
the error case if the received frame is to long.
The frame size notification came from code in the SIS driver, and
the support for long frames derived from the NetBSD Tulip driver.
Tested on: 4 port D-Link adapter DFE-570TX 4 Intel 21143
Netgear card with 82c169 PNIC 10/100BaseTX
Reviewed by: ru (manpage), wpaul (not objected to), archie
Approved by: imp
Obtained from: NetBSD