Define IPPROTO_ETHERNET on Linux-like platforms.

Define the `IPPROTO_ETHERNET` constant on Linux-like platforms.

This value is also now a registered protocol number IANA, called "Ethernet":

https://www.iana.org/assignments/protocol-numbers/protocol-numbers.xhtml

Author: sunfishcode

libc-test/build.rs

@@ -1799,7 +1799,7 @@ fn test_android(target: &str) {
             | "MADV_POPULATE_WRITE" => true,
 
             // kernel 5.6 minimum required
-            "IPPROTO_MPTCP" => true,
+            "IPPROTO_MPTCP" | "IPPROTO_ETHERNET" => true,
 
             _ => false,
         }
@@ -3578,6 +3578,7 @@ fn test_linux(target: &str) {
 
             // IPPROTO_MAX was increased in 5.6 for IPPROTO_MPTCP:
             | "IPPROTO_MAX"
+            | "IPPROTO_ETHERNET"
             | "IPPROTO_MPTCP" => true,
 
             // FIXME: Not currently available in headers

libc-test/semver/linux.txt

@@ -1041,6 +1041,7 @@ IPPROTO_DSTOPTS
 IPPROTO_EGP
 IPPROTO_ENCAP
 IPPROTO_ESP
+IPPROTO_ETHERNET
 IPPROTO_FRAGMENT
 IPPROTO_GRE
 IPPROTO_HOPOPTS

src/unix/linux_like/mod.rs

@@ -918,6 +918,8 @@ pub const IPPROTO_BEETPH: ::c_int = 94;
 pub const IPPROTO_MPLS: ::c_int = 137;
 /// Multipath TCP
 pub const IPPROTO_MPTCP: ::c_int = 262;
+/// Ethernet-within-IPv6 encapsulation.
+pub const IPPROTO_ETHERNET: ::c_int = 143;
 
 pub const MCAST_EXCLUDE: ::c_int = 0;
 pub const MCAST_INCLUDE: ::c_int = 1;