invoicesrpc: expose selectHopHints
invoicesrpc: expose selectHopHints

selectHopHints is the function which constructs hophints otherwise found
in an invoice created with the private flag.

In this commit, we expose that functionality a little more to workaround
needing to create an invoice to retrieve routing hints. Of course, this
is not a perfect solution as the functionality is exposed exclusively to
go users.

aakselrod/lnd,aakselrod/lnd