Added missing net_tstamp.h header to tests.

Signed-off-by: Gerd Zellweger <mail@gerdzellweger.com>

libc-test/build.rs

@@ -281,6 +281,7 @@ fn main() {
         cfg.header("linux/seccomp.h");
         cfg.header("linux/if_ether.h");
         cfg.header("linux/if_tun.h");
+        cfg.header("linux/net_tstamp.h");
         // DCCP support
         if !uclibc && !musl && !emscripten {
             cfg.header("linux/dccp.h");