brcm80211: fmac: remove primary mac address handling from brcmf_net_attach

The mac address for the primary interface was handled different from
the other interfaces. The code has been restructured such that the
brcmf_net_attach function treats the interfaces equal.

Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>