Check roles in OPEN and prevent route leaks with Only to Customer (RFC 9234)

A peer's configured role now does three more things:

- Our OPEN carries the BGP Role capability with what we are to the peer.
  A peer whose own says it is something that does not pair with that, or
  that sends two different roles, is refused with OPEN Message Error /
  Role Mismatch. A peer that says nothing is accepted unless require_role
  is set. A role on a peer in our own AS is a configuration error.
- Routes from a provider, a peer or a route server are marked Only to
  Customer on the way in if they are not already, and our routes are
  marked on the way out to a customer, a peer or a route server client.
- A marked route from a customer or route server client, or from a peer
  with someone else's mark, is a leak and is refused. No policy setting
  turns that off.

The packet crate gains the Only to Customer attribute (malformed:
treat-as-withdraw), and the Role Mismatch subcode is corrected from 8 to
11.

The status page shows whether the peer confirmed its role.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

crates/integration-tests/tests/dialer.rs

@@ -36,6 +36,7 @@ async fn server_dialing(listener: &TcpListener, remote_asn: u32) -> Result<TestS
             add_path: None,
             import: ImportPolicy::permissive(),
             role: None,
+            require_role: false,
         }];
     })
     .await
@@ -192,6 +193,7 @@ async fn test_inbound_from_configured_address_uses_config() -> Result<()> {
             add_path: None,
             import: ImportPolicy::permissive(),
             role: None,
+            require_role: false,
         }];
     })
     .await?;
@@ -242,6 +244,7 @@ async fn test_local_address_is_used_as_the_source() -> Result<()> {
             add_path: None,
             import: ImportPolicy::permissive(),
             role: None,
+            require_role: false,
         }];
     })
     .await?;
@@ -261,6 +264,7 @@ async fn test_local_address_is_used_as_the_source() -> Result<()> {
             add_path: None,
             import: ImportPolicy::permissive(),
             role: None,
+            require_role: false,
         }];
     })
     .await?;