It seems that RealTek 8129/8139 chip reports invalid length of

It seems that RealTek 8129/8139 chip reports invalid length of
received frame under certain conditions. wpaul said the length
0xfff0 is special meaning that indicates hardware is in the
process of copying a packet into host memory. But it seems
there are other cases that hardware is busy or stuck in bad
situation even if the received frame length is not 0xfff0.
To work-around this condition, add a check that verifys that
recevied frame length is in valid range. If received length is out
of range reinitialize hardware to recover from stuck condition.

Reported by:	Mike Tancsa ( mike AT sentex DOT net )
Tested by:	Mike Tancsa
Obtained from:	OpenBSD
MFC after:	1 week