pay-plugin: set gossmods directly

Multiple places in the pay lifecycle depend on mods to be set. By
setting the mods directly after the first listpeerchannels call,
subsequent calls to listpeerchannels are avoided.

Changelog-Fixed: pay-plugin: only call listpeerchannels once during a
payment lifecycle.

plugins/libplugin-pay.c

@@ -2603,6 +2603,8 @@ local_channel_hints_listpeerchannels(struct command *cmd, const char *buffer,
 	 * otherwise start out as excluded and remain so until
 	 * forever. */
 	channel_hint_set_update(payment_root(p)->hints, time_now());
+	p->mods = gossmods_from_listpeerchannels(
+	    p, p->local_id, buffer, toks, true, gossmod_add_localchan, NULL);
 
 	payment_continue(p);
 	return command_still_pending(cmd);