These were so far only used for bolt11 construction, but we'll need them for the
DNS seed as well, so here we just pull them out into their own unit and prefix
them.
Signed-off-by: Christian Decker <decker.christian@gmail.com>
We can have more than one; eg we might offer both bech32 and a p2sh
address, and in future we might offer v1 segwit, etc.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
I didn't convert all tests: they can still use a standalone context.
It's just marginally more efficient to share the libwally one for all
our daemons which link against it anyway.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>