Due to multiple calls of add interface routine, vif is getting duplicated
and at certain instance, we are out of vifs, causing the driver to behave
abnormal.

Fix: Every vif has a unique mac-id, when we got a vif with same mac-id as
the previous id's, we will override the respective vif.
Signed-off-by: Siva Rebbagondla <siva.rebbagondla@redpinesignals.com>
Signed-off-by: Sushant Kumar Mishra <sushant.mishra@redpinesignals.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>