Update to v5.0 kernel headers.

Test: Builds and boots on taimen.
Change-Id: I13843bf1ab30ea89a50852adc88f2cba8401bded
diff --git a/libc/kernel/uapi/linux/snmp.h b/libc/kernel/uapi/linux/snmp.h
index ae24f0f..75dea54 100644
--- a/libc/kernel/uapi/linux/snmp.h
+++ b/libc/kernel/uapi/linux/snmp.h
@@ -210,6 +210,7 @@
   LINUX_MIB_TCPREQQFULLDROP,
   LINUX_MIB_TCPRETRANSFAIL,
   LINUX_MIB_TCPRCVCOALESCE,
+  LINUX_MIB_TCPBACKLOGCOALESCE,
   LINUX_MIB_TCPOFOQUEUE,
   LINUX_MIB_TCPOFODROP,
   LINUX_MIB_TCPOFOMERGE,