First install the b43-firmware package from the AUR, then reboot, this should get it to work even without the dkms pkg you installed.
Also see 2009 macbook pro install fail - #4 by cscs and the linked B43 driver seems to be installed, but no place to check "enable wifi" in new install? - #43 by 6x12 or check other threads about Mac’s broadcom issues:
Search results for 'b43 @6x12' - Manjaro Linux Forum