The eth_disable function has to make sure that the ethernet card is not
receiving/transmitting packets anymore. The eth_enable function has to
re-enable the ethernet card after L4Linux was terminated.

		| tested on			| eth_disable/eth_enable
----------------+-------------------------------+------------------------
eepro100	| antonia			|         ok
tulip		| christian			|         ok
pcnet32		| VMware			|         ok
3c595		|				|
3c509		|				|
3c90x		|				|
rtl8139		|				|     not working

