6.2 mtu now limits size of incomming packet

[Mike Karels]

> There are also things to consider such as if a GigE card is connected to 
> a GigE device (switch/card etc) and the card supports jumbo frames 
> should the MRU be set to the max jumbo receive size for the card? This 
> could cause confusion when people plug jumbo capable devices in with 
> hardware limitations making the MRU lower than other devices on the network.

Although we don't have an MRU explicitly, we don't enable reception
of jumbo frames without administrator action.  There is an IFCAP_JUMBO_MTU
flag defined, but not previously used as far as I know.  We added the
ability to set that flag with ifconfig, which enables reception of
jumbo frames without changing the MTU.  Then, in ether_input, we accept
any packet that a NIC sees fit to receive.

		Mike