tools headers UAPI: Sync linux/in.h copy with the kernel sources

To pick the changes in:

  3218274 ("icmp: don't send out ICMP messages with a source address of 0.0.0.0")

That don't result in any change in tooling, as INADDR_ are not used to
generate id->string tables used by 'perf trace'.

This addresses this build warning:

  Warning: Kernel ABI header at 'tools/include/uapi/linux/in.h' differs from latest version at 'include/uapi/linux/in.h'
  diff -u tools/include/uapi/linux/in.h include/uapi/linux/in.h

Cc: David S. Miller <davem@davemloft.net>
Cc: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Author: acmel

tools/include/uapi/linux/in.h

@@ -289,6 +289,9 @@ struct sockaddr_in {
 /* Address indicating an error return. */
 #define	INADDR_NONE		((unsigned long int) 0xffffffff)
 
+/* Dummy address for src of ICMP replies if no real address is set (RFC7600). */
+#define	INADDR_DUMMY		((unsigned long int) 0xc0000008)
+
 /* Network number for local host loopback. */
 #define	IN_LOOPBACKNET		127