s390/net: set HW port number in netdevice

struct net_device contains a dev_port field. Store the OSA port number
in this field.

Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
Reviewed-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>