Ignore unsupported telnet subnegotiation payload until `IAC SE` so
option bytes do not leak into the first NSH command.
Keep existing NAWS handling intact and also treat `IAC IAC` inside
subnegotiation payload as an escaped `0xFF` data byte rather than a
subnegotiation terminator.
This makes subnegotiation parsing RFC-compliant for both unsupported
options and NAWS payload processing.
Signed-off-by: Shunchao Hu <ankohuu@gmail.com>
Shunchao Hu
b86b309eea