channeld: rename onion_message to obs_onion_message.

This splits the existing old-spec pathways to prepare for the
new ones.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

devtools/blindedpath.c

@@ -146,7 +146,7 @@ int main(int argc, char **argv)
 			inner = tlv_encmsg_tlvs_new(tmpctx);
 			/* Use scid if they provided one */
 			if (scids[i]) {
-				inner->next_short_channel_id
+				inner->obs_next_short_channel_id
 					= tal_dup(inner, struct short_channel_id,
 						  scids[i]);
 			} else {