staging: wilc1000: use RCU list to maintain vif interfaces list

staging: wilc1000: use RCU list to maintain vif interfaces list

Make use of RCU list to maintain virtual interfaces instead of an array.
The update operation on 'vif' list is less compare to the read
operations. Mostly the 'vif' list elements are accessed for the read
operation, so RCU list is more suited for this requirement.
The shifting of interface index id's during the delete interface is not
required. As the firmware only supports 2 interfaces so make use of
available free slot index id during add interface.

Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Link: https://lore.kernel.org/r/20190926151436.27819-3-ajay.kathat@microchip.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>