bpf/selftests: test_select_reuseport_kern: remove unused header

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

---
I stumbled upon this specific header include while trying to build selftests on the current bpf-next_base branch, which ended with this error:

[...]
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;

The exact error (unknown TC mode) is likely rather due to some issues in my local build, in which I am actually cross-compiling selftests (for ARM64 from a x86_64 host, but not through vmtests.sh), and I still have to sort out some other issues. But I guess it is not really right anyway to include stdlib.h from an ebpf program, especially if it is not used, so I am still proposing this small change.

---
 tools/testing/selftests/bpf/progs/test_select_reuseport_kern.c | 1 -
 1 file changed, 1 deletion(-)

index 5eb25c6ad75b1a9c61f22e978d817d3dc88b3a2f..a5be3267dbb01372c84bb468e3a48eae69ac5329 100644
@@ -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>

---
base-commit: 072c40912477ebac2ef98cd0b1532ba9bebda20a
change-id: 20250227-remove_wrong_header-02d288d64204

Best regards,

Alexis Lothoré, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com