[PATCH net v2] uapi: Add missing linux/stddef.h header file to in.h

[Yang Jihong]

commit 5854a09b4957 ("net/ipv4: Use __DECLARE_FLEX_ARRAY() helper") does
not include "linux/stddef.h" header file, and tools headers update
linux/in.h copy, BPF prog fails to be compiled:

    CLNG-BPF [test_maps] bpf_flow.bpf.o
    CLNG-BPF [test_maps] cgroup_skb_sk_lookup_kern.bpf.o
  In file included from progs/cgroup_skb_sk_lookup_kern.c:9:
  /root/linux/tools/include/uapi/linux/in.h:199:3: error: type name requires a specifier or qualifier
                  __DECLARE_FLEX_ARRAY(__be32, imsf_slist_flex);
                  ^
  /root/linux/tools/include/uapi/linux/in.h:199:32: error: type specifier missing, defaults to 'int' [-Werror,-Wimplicit-int]
                  __DECLARE_FLEX_ARRAY(__be32, imsf_slist_flex);
                                               ^
  2 errors generated.

To maintain consistency, add missing header file to kernel.

Fixes: 5854a09b4957 ("net/ipv4: Use __DECLARE_FLEX_ARRAY() helper")
Signed-off-by: Yang Jihong <yangjihong1@xxxxxxxxxx>
---

Changes since v1:
 - 'Fixes' tag separates by the commit message by a blank line
 - Remove the empty line between 'Fixes' and SoB.
 - Specify the target tree to "net" in title
 - Wrap the commit message text to 75 chars per line (except build output)

 include/uapi/linux/in.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/include/uapi/linux/in.h b/include/uapi/linux/in.h
index f243ce665f74..79015665daf1 100644
--- a/include/uapi/linux/in.h
+++ b/include/uapi/linux/in.h
@@ -22,6 +22,7 @@
 #include <linux/types.h>
 #include <linux/libc-compat.h>
 #include <linux/socket.h>
+#include <linux/stddef.h>
 
 #if __UAPI_DEF_IN_IPPROTO
 /* Standard well-defined IP protocols.  */
-- 
2.30.GIT