broadcom-wl: change interface names

'netifd' treats all devices with a "." in their name as vlan devices.
Modify the name of virtual/WDS interfaces created by broadcom-wl to use
a "-" instead of a ".", so they will be treated as simple devices
by 'netifd'.

Signed-off-by: Nathan Hintz <nlhintz@hotmail.com>

SVN-Revision: 38748