Review sysctl settings

[troglobit]

mDNS currently runs on all layer-3 interfaces when enabled. The Styx board has 28 ports, with many set up as L3 interfaces we get the following error:

 Nov 18 14:54:56 styx-05-29-61 avahi-daemon[7483]: IP_ADD_MEMBERSHIP failed: No buffer space available

This is caused by the Linux sysctl net.ipv4.igmp_max_memberships default limit of 20.

While researching the topic the following links popped up:

• Cumulus Linux default sysctl.conf https://gist.github.com/ericpulvino/48405354a6d417a1375b49d4f4545408
• Frr sysctl.conf recommendations for routing: https://github.com/FRRouting/frr/blob/master/doc/user/Useful_Sysctl_Settings.md

Most of the changes are very relevant also for Infix. We need to investigate and update at least net.ipv4.igmp_max_memberships.