tls-endpoint: allow an ip to listen on being specified on command line

[hannesm]

for fixing the other part of #143 (or the suggestion in it)

[hannesm]

So, what is the opinion on this PR? We could:

• just close it (until someone requests such a feature)
• in the bind have code paths depending on the ip protocol version provided
• just remove albatross_tls_endpoint (and advertise the inetd service more)
• select a single ip protocol version to use

What do you think @reynir? I'm fine with option 2 since it seems to solve the remaining issues.

[hannesm]

I propose a307e58 (part of this PR), and think this can be merged and shouldn't exhibit strange behaviour.