logmsgbot: only allow connections from tin, fenari & localhost

It'd be nicer to be a bit more permissive here and allow our full internal IP
ranges. Using single-address IPv6 CIDR ranges to specify single IPv4 IPs is a
bit ugly. But this is OK for now, I think.

Tested.

Change-Id: Ib33d3cc666f9c1ca0848ae067f3047d8b7939d3e