Revert "TelnetClient ignores requests for already entered modes"

This reverts commit cfce5e67437fd049ffcedf198b17737fac3c6e34.
TelnetClient denies request for unsupported option

TelnetClient denies request to begin performing an unsupported
TELNET option by sending a negative acknowledgment (WONT).
TelnetClient acknowledges NEW-ENVIRON option