libertas: separate mesh connectivity from that of the main interface

The transmit and receive traffic as soon as the mesh interface is
brought up.

Test case 1:  Bring up only the mesh interface and ping.  No need for
any iwconfig commands on the main interface.

$ ifconfig msh0 192.168.5.3
$ iwconfig msh0 channel X
$ ping 192.168.5.2
If ping succeeds, PASS

Test case 2:  Associate with the main interface, and turn off AP.  Mesh
interface should not lose connectivity.

$ iwconfig eth0 mode managed essid "my_ssid"
$ ifconfig msh0 192.168.5.3
$ ping 192.168.5.2
<turn off access point>
If ping continues uninterrupted, PASS

This feature requires firmware version 5.110.19.p0 or newer, available
here: http://dev.laptop.org/pub/firmware/libertas/



Signed-off-by: Ashish Shukla <ashishs@marvell.com>
Signed-off-by: Javier Cardona <javier@cozybit.com>
Signed-off-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>