Advertise segwit support

Now that commitments can be handled.

src/bitcoin.c

@@ -17,7 +17,7 @@
 
 static const char *b58chars = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz";
 
-static char* understood_rules[] = {};
+static char* understood_rules[] = {"segwit"};
 static bool check_required_rule(const char* rule)
 {
 	unsigned int i;
@@ -90,7 +90,7 @@ out:
 	return ret;
 }
 
-static const char *gbt_req = "{\"method\": \"getblocktemplate\", \"params\": [{\"capabilities\": [\"coinbasetxn\", \"workid\", \"coinbase/append\"]}]}\n";
+static const char *gbt_req = "{\"method\": \"getblocktemplate\", \"params\": [{\"capabilities\": [\"coinbasetxn\", \"workid\", \"coinbase/append\"], \"rules\" : [\"segwit\"]}]}\n";
 
 /* Request getblocktemplate from bitcoind already connected with a connsock_t
  * and then summarise the information to the most efficient set of data