brcmfmac: set interface carrier to off by default

It's important as brcmfmac creates one main interface for each PHY and
doesn't allow deleting it. Not setting carrier could result in other
subsystems misbehaving (e.g. LEDs "netdev" trigger turning LED on).

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>