Fix cmp::max execution in ChannelContext::get_dust_buffer_feerate

  The current `cmp::max` doesnt align with the function comment, ie its
  comparing 2530 and `feerate_plus_quarter` instead of `feerate_per_kw
  + 2530` and `feerate_plus_quarter` which is fixed in this commit

Author: jbesraa

lightning/src/ln/channel.rs

@@ -2699,7 +2699,7 @@ impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider  {
 			feerate_per_kw = cmp::max(feerate_per_kw, feerate);
 		}
 		let feerate_plus_quarter = feerate_per_kw.checked_mul(1250).map(|v| v / 1000);
-		cmp::max(2530, feerate_plus_quarter.unwrap_or(u32::max_value()))
+		cmp::max(feerate_per_kw + 2530, feerate_plus_quarter.unwrap_or(u32::max_value()))
 	}
 
 	/// Get forwarding information for the counterparty.