feat: add min_capacity_sat config value and switch

- add config value min_capacity_sat that will replaces the magic value
  min_effective_htlc_capacity = AMOUNT_MSAT(1000000)
- add config switch min_capacity_sat

lightningd/lightningd.h

@@ -67,6 +67,9 @@ struct config {
 
 	/* Are we allowed to use DNS lookup for peers. */
 	bool use_dns;
+
+	/* Minimal amount of effective funding_satoshis for accepting channels */
+	u64 min_capacity_sat;
 };
 
 struct lightningd {

lightningd/opening_control.c

@@ -662,8 +662,10 @@ static void channel_config(struct lightningd *ld,
 {
 	/* FIXME: depend on feerate. */
 	*max_to_self_delay = ld->config.locktime_max;
-	/* This is 1c at $1000/BTC */
-	*min_effective_htlc_capacity = AMOUNT_MSAT(1000000);
+
+	/* Take minimal effective capacity from config min_capacity_sat */
+	amount_msat_from_sat_u64(min_effective_htlc_capacity,
+		ld->config.min_capacity_sat);
 
 	/* BOLT #2:
 	 *

lightningd/options.c

@@ -376,6 +376,9 @@ static void config_register_opts(struct lightningd *ld)
 	opt_register_arg("--fee-per-satoshi", opt_set_u32, opt_show_u32,
 			 &ld->config.fee_per_satoshi,
 			 "Microsatoshi fee for every satoshi in HTLC");
+	opt_register_arg("--min-capacity-sat", opt_set_u64, opt_show_u64,
+			 &ld->config.min_capacity_sat,
+			 "Minimum capacity in satoshis for accepting channels");
 	opt_register_arg("--addr", opt_add_addr, NULL,
 			 ld,
 			 "Set an IP address (v4 or v6) to listen on and announce to the network for incoming connections");
@@ -544,6 +547,9 @@ static const struct config testnet_config = {
 	.max_fee_multiplier = 10,
 
 	.use_dns = true,
+
+	/* Sets min_effective_htlc_capacity - at 1000$/BTC this is 1ct */
+	.min_capacity_sat = 1000,
 };
 
 /* aka. "Dude, where's my coins?" */
@@ -607,6 +613,9 @@ static const struct config mainnet_config = {
 	.max_fee_multiplier = 10,
 
 	.use_dns = true,
+
+	/* Sets min_effective_htlc_capacity - at 1000$/BTC this is 1ct */
+	.min_capacity_sat = 1000,
 };
 
 static void check_config(struct lightningd *ld)

wallet/test/test_utils.c

@@ -22,4 +22,5 @@ const struct config test_config = {
 	.rescan = 30,
 	.max_fee_multiplier = 10,
 	.use_dns = true,
+	.min_capacity_sat = 1000,
 };