brcmfmac: do not disconnect for disassoc frame from unconnected AP

Ignore FW event if the event's BSSID is different form the BSSID of the
currently connected AP. Check interface state is connected or not, if
state is not connected that can ignore link down event.

Signed-off-by: Able Liao <Able.Liao@cypress.com>
Signed-off-by: Chi-hsien Lin <chi-hsien.lin@cypress.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200618160739.21457-4-chi-hsien.lin@cypress.com