crimson/net: change ConnectionRef to be a local_shared_foreign_ptr

crimson/net: change ConnectionRef to be a local_shared_foreign_ptr

Make it possible for connections and messages to be dispatched in
arbitrary core without asynchronous foreign copy.

The local_shared_foreign_ptr conn cannot be moved to another core
implicitly, maintain it outside Message independently.

Do asynchronous foreign copy to the new ConnectionRef only in
with_remote_shard_state_and_op().

Signed-off-by: Yingxin Cheng <yingxin.cheng@intel.com>