[NET]: Change 1500 to ETH_DATA_LEN in some files

These patches add the header linux/if_ether.h and change 1500 to
ETH_DATA_LEN in some files.

Signed-off-by: Kris Katterjohn <kjak@users.sourceforge.net>
Signed-off-by: David S. Miller <davem@davemloft.net>