[PATCH] cleanup large frame handling for natsemi.c

[Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>]

Hi,

The DP83815/6 by default rejects frames longer that 1518 bytes 
(including crc). This means that a special flag must be set for 8021q - 
otherwise mtu sized packets are dropped.
The current driver enables this flag only if the buffer size is above 
1536 bytes - this is wrong. Additionally, the nic writes up to two bytes 
behind the indicated end of the buffer. This is not documented, thus 
I've added 64 bytes - just to be safe.
The patch also removes RX_OFFSET from the rx buffer allocation: The nic 
can only receive to 32-bit aligned addresses, it's a left over from a 
skeleton driver.
Jeff, could you apply it? I've stress tested vlan for an hour with 
tbench and parallel kernel compiles, not obvious problems.
--
   Manfred