drivers/net: ks8842 Fix crash on received packet when in PIO mode.

This patch fixes a driver crash during packet reception due to not enough
bytes allocated in the skb. Since the loop reads out 4 bytes at a time, we
need to allow for up to 3 bytes of slack space.

Signed-off-by: Dennis Aberilla <denzzzhome@yahoo.com>
Signed-off-by: David S. Miller <davem@zippy.davemloft.net>