qeth: Display adjacent switch attributes

Add support to display the adjacent switch port's forwarding
attributes. Currently supports info on forwarding modes '802.1'
and 'rr' (reflective relay).

Signed-off-by: Stefan Raspl <raspl@linux.vnet.ibm.com>
Signed-off-by: Frank Blaschka <blaschka@linux.vnet.ibm.com>
Reviewed-by: Ursula Braun <ursula.braun@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>