[PATCH bpf-next v1 12/19] selftests/bpf: Fix compiling kfree_skb.c with musl-libc

[Tony Ambardar <tony.ambardar@xxxxxxxxx>]

The GNU version of 'struct tcphdr' with member 'doff' is not exposed by
musl headers unless _GNU_SOURCE is defined. Add this definition to fix
errors seen compiling for mips64el/musl-libc:

  In file included from kfree_skb.c:2:
  kfree_skb.c: In function 'on_sample':
  kfree_skb.c:45:30: error: 'struct tcphdr' has no member named 'doff'
     45 |         if (CHECK(pkt_v6->tcp.doff != 5, "check_tcp",
        |                              ^

Fixes: 580d656d80cf ("selftests/bpf: Add kfree_skb raw_tp test")
Signed-off-by: Tony Ambardar <tony.ambardar@xxxxxxxxx>
---
 tools/testing/selftests/bpf/prog_tests/kfree_skb.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/kfree_skb.c b/tools/testing/selftests/bpf/prog_tests/kfree_skb.c
index c07991544a78..34f8822fd221 100644
--- a/tools/testing/selftests/bpf/prog_tests/kfree_skb.c
+++ b/tools/testing/selftests/bpf/prog_tests/kfree_skb.c
@@ -1,4 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
 #include <test_progs.h>
 #include <network_helpers.h>
 #include "kfree_skb.skel.h"
-- 
2.34.1