This introduces basic support for TN3270, which needs to negotiate
three Telnet options during handshake:
  - End of Record
  - Binary Transmission
  - Terminal-Type

As a basic implementation, this simply ignores NOP and Interrupt
Process(IP) commands. More work should be done for them later.

For more details, please refer to RFC 854 and 1576.
Signed-off-by: NJing Liu <liujbjl@linux.vnet.ibm.com>
Signed-off-by: NYang Chen <bjcyang@linux.vnet.ibm.com>
Reviewed-by: NQingFeng Hao <haoqf@linux.vnet.ibm.com>
Acked-by: NDong Jia Shi <bjsdjshi@linux.vnet.ibm.com>
Signed-off-by: NCornelia Huck <cornelia.huck@de.ibm.com>
Reviewed-by: NMarc-André Lureau <marcandre.lureau@redhat.com>