setchannel: add minhtlc

Suggested by @m-schmook, I realized that if we append it later I'll
never get it right: I expect parameters min and max, not max and min!

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Added: Protocol: you can now alter the `htlc_minimum_msat` and `htlc_maximum_msat` your node advertizes.

contrib/pyln-client/pyln/client/lightning.py

@@ -1176,7 +1176,7 @@ class LightningRpc(UnixDomainSocketRpc):
         }
         return self.call("setchannelfee", payload)
 
-    def setchannel(self, id, feebase=None, feeppm=None, htlcmax=None, enforcedelay=None):
+    def setchannel(self, id, feebase=None, feeppm=None, htlcmin=None, htlcmax=None, enforcedelay=None):
         """Set configuration a channel/peer {id} (or 'all').
 
         {feebase} is a value in millisatoshi that is added as base fee
@@ -1185,6 +1185,9 @@ class LightningRpc(UnixDomainSocketRpc):
         {feeppm} is a value added proportionally per-millionths to any
         routed payment volume in satoshi.
 
+        {htlcmin} is the minimum (outgoing) htlc amount to allow and
+        advertize.
+
         {htlcmax} is the maximum (outgoing) htlc amount to allow and
         advertize.
 
@@ -1196,6 +1199,7 @@ class LightningRpc(UnixDomainSocketRpc):
             "id": id,
             "feebase": feebase,
             "feeppm": feeppm,
+            "htlcmin": htlcmin,
             "htlcmax": htlcmax,
             "enforcedelay": enforcedelay,
         }