When running "fastd -v" fails, line may be NULL, causing a segfault in
strncmp.

This is currently only implemented in the gluon-mesh-vpn-fastd
package.

Advertising the public key may be deemed problematic when
your threat-model involves protecting the nodes privacy
from tunnel traffic correlation by onlink observers.

It can be enabled by setting site.mesh_vpn.fastd.pubkey_privacy
to `false`.

by moving the declaration of ret to the top of get_fastd()

Fixes #1130

Most doubles that are delivered via respondd have limited input
precision, but are converted with up to 17 digits of precision. That can
cause ugly blowups like 0.2800000000000001 in the output, which is
avoided by specifying better format strings (like "%.2f" in most cases).

gluon-announced and gluon-announce are merged to gluon-respondd.