accept_forwards_to_priv_channels is always false

[TheBlueMatt]

default_user_config sets user_config.accept_forwards_to_priv_channels = false; if !may_announce_channel(config) but it also defaults to false, so its always false.

[tnull]

Hmm, good catch. But, I'm kind of confused why we didn't hit this before in testing. I guess accept_forwards_to_priv_channels does not apply for intercepted payments that we manually forward.

[tnull]

Now opened #503