Update to v4.19 kernel headers.

Test: Builds and boots.
Change-Id: I99a9ed79666e143b47f02ca4e59eed94f69b7e4a
(cherry picked from commit a981e2e52e2e95a65fa9c9b6fb16dcb4c83dd576)
diff --git a/libc/kernel/uapi/linux/net_tstamp.h b/libc/kernel/uapi/linux/net_tstamp.h
index 49d4c2c..2f022ea 100644
--- a/libc/kernel/uapi/linux/net_tstamp.h
+++ b/libc/kernel/uapi/linux/net_tstamp.h
@@ -73,4 +73,14 @@
   __u32 pkt_length;
   __u32 reserved[2];
 };
+enum txtime_flags {
+  SOF_TXTIME_DEADLINE_MODE = (1 << 0),
+  SOF_TXTIME_REPORT_ERRORS = (1 << 1),
+  SOF_TXTIME_FLAGS_LAST = SOF_TXTIME_REPORT_ERRORS,
+  SOF_TXTIME_FLAGS_MASK = (SOF_TXTIME_FLAGS_LAST - 1) | SOF_TXTIME_FLAGS_LAST
+};
+struct sock_txtime {
+  clockid_t clockid;
+  __u32 flags;
+};
 #endif