char: set name for all I/O channels created

Ensure that all I/O channels created for character devices
are given names to distinguish their respective roles.

Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>