wil6210: drop Rx multicast packets that are looped-back to STA

Delivering a looped-back multicast packet to network stack can cause
higher layer protocols to fail like for example IPv6 DAD.
In STA mode, upon receiving Rx multicast packet, check if the source
MAC address is equal to our own MAC address and if so drop the packet.

Signed-off-by: Dedy Lansky <dlansky@codeaurora.org>
Signed-off-by: Maya Erez <merez@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>