it seems the brcmsmac driver creates a device whose direct parent doesn't report that it's a pci device, so udev's net_id builtin moves past the NET_PCI naming and instead uses the NET_BCMA naming, since it's a BCMA device. That naming format is the same as pci, but appends bcma_core, which is set to 'b%u' for all cores > 0.
it seems the brcmsmac driver creates a device whose direct parent doesn't report that it's a pci device, so udev's net_id builtin moves past the NET_PCI naming and instead uses the NET_BCMA naming, since it's a BCMA device. That naming format is the same as pci, but appends bcma_core, which is set to 'b%u' for all cores > 0.