Ethernet pads frames to 60 bytes minimum; without an explicit length
field the receiver cannot distinguish real payload from zero padding
(e.g. a 6-byte DISCOVER becomes 46 bytes after padding, failing the
'payload must be empty' check).
Header is now 8 bytes: [ver:1][type:1][session_id:4][payload_len:2]
(both multi-byte fields big-endian). The receiver slices exactly
payload_len bytes and ignores trailing padding.
Updated PROTOCOL.md, Rust frame.rs, and C# Frame.cs.
- io::last_os_error() -> io::Error::last_os_error()
- MacAddr(mac.0) -> MacAddr(mac.octets()) for pnet 0.35
- cast htons() result to c_int for libc::socket protocol arg
- mark read as mut in spawn_pump
mute