bridge: fix build for CONFIG_SYSFS disabled

Fix build when CONFIG_SYSFS is not enabled:
net/bridge/br_if.c:136: error: 'struct net_bridge_port' has no member named 'sysfs_name'

Note: dev->name == sysfs_name except when change name is in
progress, and we are protected from that by RTNL mutex.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Acked-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>