qeth: bridgeport support - basic control

Introduce functions to assign roles and check state of bridgeport-capable
HiperSocket devices, and sysfs attributes providing access to these
functions from userspace. Introduce udev events emitted when the state
of a bridgeport device changes.

Signed-off-by: Eugene Crosser <eugene.crosser@ru.ibm.com>
Signed-off-by: Frank Blaschka <frank.blaschka@de.ibm.com>
Reviewed-by: Ursula Braun <ursula.braun@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>