Mhh. Finally it has created the bridge interface:
Tue Jul 27 12:36:45 2021
daemon.info openwisp: Local configuration outdated
Tue Jul 27 12:36:45 2021
daemon.info openwisp: Downloading configuration from controller...
Tue Jul 27 12:36:45 2021
daemon.info openwisp: Configuration downloaded, now applying it...
Tue Jul 27 12:36:45 2021
daemon.info openwisp: Service network has been reloaded via procd/ubus
Tue Jul 27 12:36:45 2021
daemon.info openwisp: Service wireless has been reloaded via procd/ubus
Tue Jul 27 12:36:48 2021
kern.info kernel: [ 7507.267951] br-bb: port 1(eth0.3170) entered blocking state
Tue Jul 27 12:36:48 2021
kern.info kernel: [ 7507.273698] br-bb: port 1(eth0.3170) entered disabled state
Tue Jul 27 12:36:48 2021
kern.info kernel: [ 7507.279612] device eth0.3170 entered promiscuous mode
Tue Jul 27 12:36:48 2021
kern.info kernel: [ 7507.320461] br-bb: port 1(eth0.3170) entered blocking state
Tue Jul 27 12:36:48 2021
kern.info kernel: [ 7507.326158] br-bb: port 1(eth0.3170) entered forwarding state
Tue Jul 27 12:36:48 2021 daemon.notice netifd: Interface 'bb' is enabled
Tue Jul 27 12:36:48 2021 daemon.notice netifd: bridge 'br-bb' link is up
Tue Jul 27 12:36:48 2021 daemon.notice netifd: Interface 'bb' has link connectivity
Tue Jul 27 12:36:48 2021 daemon.notice netifd: Interface 'bb' is setting up now
Tue Jul 27 12:36:49 2021 daemon.notice netifd: Interface 'bb' is now up
Tue Jul 27 12:36:49 2021 daemon.notice netifd: VLAN 'eth0.3170' link is up
Tue Jul 27 12:36:49 2021 daemon.notice hostapd: wlan0: interface state ENABLED->DISABLED
Tue Jul 27 12:36:49 2021 daemon.notice hostapd: wlan0: AP-DISABLED
Tue Jul 27 12:36:49 2021 daemon.notice hostapd: wlan0: CTRL-EVENT-TERMINATING
Tue Jul 27 12:36:49 2021 daemon.notice hostapd: nl80211: deinit ifname=wlan0 disabled_11b_rates=0
Tue Jul 27 12:36:51 2021
daemon.info openwisp: Testing configuration...
Tue Jul 27 12:36:51 2021
daemon.info openwisp: Configuration test succeeded
Tue Jul 27 12:36:51 2021
daemon.info openwisp: Configuration applied successfully
So it's solved.