base-files: config_generate: split macaddr with multiple ifaces

base-files: config_generate: split macaddr with multiple ifaces

netifd does not handle network.@device[x].name properly if it
contains multiple ifaces separated by spaces. Due to this, board.d
lan_mac setup does not work if multiple ifaces are set to LAN by
ucidef_set_interface_lan.

To fix this, create a device node for each member iface when
running config_generate instead. Those are named based on the
member ifname:

  ucidef_set_interface_lan "eth0 eth1.1"
  ucidef_set_interface_macaddr "lan" "yy:yy:yy:yy:yy:01"

will return

  config device 'lan_eth0_dev'
        option name 'eth0'
        option macaddr 'yy:yy:yy:yy:yy:01'

  config device 'lan_eth1_1_dev'
        option name 'eth1.1'
        option macaddr 'yy:yy:yy:yy:yy:01'

ref: https://github.com/openwrt/openwrt/pull/2542

Signed-off-by: Sungbo Eo <mans0n@gorani.run>
[always use new scheme, extend description, change commit title]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
(cherry picked from commit 298814e6be7640d89328de9e7c90d4349e30683f)