qtnfmac: control qtnfmac wireless interfaces bridging

Bridging qtnfmac interfaces is possible only if the following two
conditions are fulfilled:
- firmware advertises proper support with QLINK_HW_CAPAB_HW_BRIDGE
- kernel is built with CONFIG_NET_SWITCHDEV support

Otherwise adding qtnfmac wireless interfaces into the same bridge
should not be allowed since packets flooded by kernel may break
internal forwarding rules between interfaces.

This patch disables adding qtnfmac wireless interfaces into the
same bridge if no support is provided either by card or by kernel.

Signed-off-by: Sergey Matyukevich <sergey.matyukevich.os@quantenna.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>