Update to v5.0 kernel headers.

Test: Builds and boots on taimen.
Change-Id: I13843bf1ab30ea89a50852adc88f2cba8401bded
diff --git a/libc/kernel/uapi/linux/tcp.h b/libc/kernel/uapi/linux/tcp.h
index d940f0f..ce3d735 100644
--- a/libc/kernel/uapi/linux/tcp.h
+++ b/libc/kernel/uapi/linux/tcp.h
@@ -207,6 +207,7 @@
   TCP_NLA_BYTES_RETRANS,
   TCP_NLA_DSACK_DUPS,
   TCP_NLA_REORD_SEEN,
+  TCP_NLA_SRTT,
 };
 #define TCP_MD5SIG_MAXKEYLEN 80
 #define TCP_MD5SIG_FLAG_PREFIX 1