Add spendable/receivable and is_local fields to the callback function
used in gossmods_from_listpeerchannels. This allows to do more fine
grained use of the listpeerchannels call.
The first use case is renepay, for which we need to ignore the htlc_max
of the local channels only.
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automatically loaded when lightningd starts (unless suppressed with
commandline options).