bpf/selftests: test_select_reuseport_kern: Remove unused header

commit 93cf4e5 upstream.

test_select_reuseport_kern.c is currently including <stdlib.h>, but it
does not use any definition from there.

Remove stdlib.h inclusion from test_select_reuseport_kern.c

Signed-off-by: Alexis Lothoré (eBPF Foundation) <alexis.lothore@bootlin.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://patch.msgid.link/20250227-remove_wrong_header-v1-1-bc94eb4e2f73@bootlin.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
[shung-hsi.yu: Fix compilation error mentioned in footer of Alexis'
patch with newer glibc header:

  [...]
    CLNG-BPF [test_progs-cpuv4] test_select_reuseport_kern.bpf.o
  In file included from progs/test_select_reuseport_kern.c:4:
  /usr/include/bits/floatn.h:83:52: error: unsupported machine mode
  '__TC__'
     83 | typedef _Complex float __cfloat128 __attribute__ ((__mode__
  (__TC__)));
        |                                                    ^
  /usr/include/bits/floatn.h:97:9: error: __float128 is not supported on
  this target
     97 | typedef __float128 _Float128;

I'm not certain when the problem starts to occur, but I'm quite sure
test_select_reuseport_kern.c were not meant to be using the C standard
library in the first place.]
Signed-off-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Tropicao

tools/testing/selftests/bpf/progs/test_select_reuseport_kern.c

@@ -1,7 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 /* Copyright (c) 2018 Facebook */
 
-#include <stdlib.h>
 #include <linux/in.h>
 #include <linux/ip.h>
 #include <linux/ipv6.h>