Update peer_connected documentation to better describe Err(())

Our `peer_connected` methods can return `Err(())` to cause the peer
to be immediately disconnected. The documentation for them,
however, only described the specific case of using this to enforce
minimal set of per feature bits.

Instead, here, we tweak the documentation to describe the
high-level utility, and only mention enforcing peer feature bits as
an example use-case.

Author: TheBlueMatt

lightning/src/ln/msgs.rs

@@ -1873,9 +1873,11 @@ pub trait BaseMessageHandler {
 
 	/// Handle a peer (re)connecting.
 	///
-	/// May return an `Err(())` if the features the peer supports are not sufficient to communicate
-	/// with us. Implementors should be somewhat conservative about doing so, however, as other
-	/// message handlers may still wish to communicate with this peer.
+	/// May return an `Err(())` to indicate that we should immediately disconnect from the peer
+	/// (e.g. because the features they support are not sufficient to communicate with us).
+	///
+	/// Note, of course, that other message handlers may wish to communicate with the peer, which
+	/// disconnecting them will prevent.
 	///
 	/// [`Self::peer_disconnected`] will not be called if `Err(())` is returned.
 	fn peer_connected(&self, their_node_id: PublicKey, msg: &Init, inbound: bool)

lightning/src/ln/peer_handler.rs

@@ -98,9 +98,11 @@ pub trait CustomMessageHandler: wire::CustomMessageReader {
 
 	/// Handle a peer connecting.
 	///
-	/// May return an `Err(())` if the features the peer supports are not sufficient to communicate
-	/// with us. Implementors should be somewhat conservative about doing so, however, as other
-	/// message handlers may still wish to communicate with this peer.
+	/// May return an `Err(())` to indicate that we should immediately disconnect from the peer
+	/// (e.g. because the features they support are not sufficient to communicate with us).
+	///
+	/// Note, of course, that other message handlers may wish to communicate with the peer, which
+	/// disconnecting them will prevent.
 	///
 	/// [`Self::peer_disconnected`] will not be called if `Err(())` is returned.
 	fn peer_connected(&self, their_node_id: PublicKey, msg: &Init, inbound: bool)