Hi Ramesh,
There are numerous reports (mostly old, afaics) of the issue you describe, but with various suggested reasons.
I suspect the avahi related part is a consequence rather than a cause - I didn't think avahi was capable of disabling interfaces, the message looks like it's updating a table/list (etc) and "...no longer relevant..." messages appear in my syslog if I deliberately disconnect from wifi.
Please can you provide syslog extracts from just before and during a time when this has happened, using:
$ sudo cat /var/log/syslog | grep -i -E "avahi|network"
(must be capital -E and no spaces around the | inside the speech marks)
Is there anything that seems relevant in
$ sudo dmesg -T
?
Out of interest, did you try running for a while with just the power management tweak?
Thanks,
Gareth