socket: add missing docs for ethernet sockets

Author: ususdei

README.md

@@ -205,7 +205,7 @@ Enable `smoltcp::phy::RawSocket` and `smoltcp::phy::TunTapInterface`, respective
 
 These features are enabled by default.
 
-### Features `socket-raw`, `socket-udp`, `socket-tcp`, `socket-icmp`, `socket-dhcpv4`, `socket-dns`
+### Features `socket-eth`, `socket-raw`, `socket-udp`, `socket-tcp`, `socket-icmp`, `socket-dhcpv4`, `socket-dns`
 
 Enable the corresponding socket type.
 

src/socket/raw.rs

@@ -82,6 +82,9 @@ pub type PacketBuffer<'a> = crate::storage::PacketBuffer<'a, ()>;
 ///
 /// A raw socket may be bound to a specific IP protocol, and owns
 /// transmit and receive packet buffers.
+///
+/// A raw socket can only handle IP-based traffic, for raw ethernet
+/// traffic look at `eth::Socket`.
 #[derive(Debug)]
 pub struct Socket<'a> {
     ip_version: Option<IpVersion>,