Posted by Gnomad on Mar 07, 2016; 2:21am
URL: https://itus.accessinnov.com/bridge-mode-not-working-tp178p316.html

In Router mode I spotted some of the same errors you mention here:

...
Mon Mar  7 10:13:10 2016 kern.err kernel: [   32.580766] drivers/rtc/hctosys.c: unable to open rtc device (rtc0)
...
Mon Mar  7 10:13:10 2016 kern.info kernel: [   50.855697] EXT3-fs (mmcblk0p2): mounted filesystem with writeback data mode
Mon Mar  7 10:13:10 2016 user.err kernel: [   51.112977] init: failed to symlink /tmp -> /var
...
Mon Mar  7 10:13:10 2016 kern.err kernel: [   29.911354] octeon-pow-ethernet ERROR: You must specify a broadcast group mask.
...

Tried what you suggested by editing /etc/config/network to fix the last one of these, but did not resolve the error (after clearing the log and a reboot)

...
config interface 'lan'
	option ifname 'eth1 eth2'
	option force_link '1'
	option type 'bridge'
	option proto 'static'
	option netmask '255.255.255.0'
	option ip6assign '60'
	option ipaddr '10.10.10.10'
	option auto '1'
	option enabled '1'
	option broadcast '10.10.10.255'

Any thoughts why that might not be picked up correctly?  
Might just add

uci set network.lan.broadcast=10.10.10.255

 to startup for now, then assume it's safe to ignore the error..