bitcoind: allow commands to be registered by different plugins

An strmap is convenient to get a plugin given a method. Populate it
while checking commands.

lightningd/bitcoind.c

@@ -1011,6 +1011,7 @@ static bool process_getblockchaininfo(struct bitcoin_cli *bcli)
 
 static void destroy_bitcoind(struct bitcoind *bitcoind)
 {
+	strmap_clear(&bitcoind->pluginsmap);
 	/* Suppresses the callbacks from bcli_finished as we free conns. */
 	bitcoind->shutdown = true;
 }
@@ -1146,6 +1147,7 @@ struct bitcoind *new_bitcoind(const tal_t *ctx,
 {
 	struct bitcoind *bitcoind = tal(ctx, struct bitcoind);
 
+	strmap_init(&bitcoind->pluginsmap);
 	bitcoind->cli = NULL;
 	bitcoind->datadir = NULL;
 	bitcoind->ld = ld;

lightningd/bitcoind.h

@@ -5,6 +5,7 @@
 #include <bitcoin/tx.h>
 #include <ccan/list/list.h>
 #include <ccan/short_types/short_types.h>
+#include <ccan/strmap/strmap.h>
 #include <ccan/tal/tal.h>
 #include <ccan/time/time.h>
 #include <ccan/typesafe_cb/typesafe_cb.h>
@@ -61,6 +62,10 @@ struct bitcoind {
 	char *rpcuser, *rpcpass, *rpcconnect, *rpcport;
 
 	struct list_head pending_getfilteredblock;
+
+	/* Map each method to a plugin, so we can have multiple plugins
+	 * handling different functionalities. */
+	STRMAP(struct plugin *) pluginsmap;
 };
 
 /* A single outpoint in a filtered block */