Fixed OFChannelHandler to always allow echo requests and replies no matter the...

Fixed OFChannelHandler to always allow echo requests and replies no matter the state in the handshake process. This issue was discovered during an unsuccessful handshake with an HP 5900af, which for whatever reason wants to handshake as follows: ... (1) FL features request, (2) HP echo request, (3) FL echo reply, (4) HP features reply. There are still issues with this switch after the handshake completes, but an echo should be honored in any state.