selftests/bpf: Fix redefinition of 'off' as different kind of symbol

This fixes the following build error

   CLNG-BPF [test_progs] verifier_global_ptr_args.bpf.o
progs/verifier_global_ptr_args.c:228:5: error: redefinition of 'off' as
different kind of symbol
   228 | u32 off;
       |     ^

The symbol 'off' was previously defined in
tools/testing/selftests/bpf/tools/include/vmlinux.h, which includes an
enum i40e_ptp_gpio_pin_state from
drivers/net/ethernet/intel/i40e/i40e_ptp.c:

	enum i40e_ptp_gpio_pin_state {
		end = -2,
		invalid = -1,
		off = 0,
		in_A = 1,
		in_B = 2,
		out_A = 3,
		out_B = 4,
	};

This enum is included when CONFIG_I40E is enabled. As of commit
032676f ("LoongArch: Update Loongson-3 default config file"),
CONFIG_I40E is set in the defconfig, which leads to the conflict.

Renaming the local variable avoids the redefinition and allows the
build to succeed.

Suggested-by: Yonghong Song <[email protected]>
Signed-off-by: Brahmajit Das <[email protected]>
Acked-by: Yonghong Song <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: listout

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

@@ -225,7 +225,7 @@ int trusted_to_untrusted(void *ctx)
 }
 
 char mem[16];
-u32 off;
+u32 offset;
 
 SEC("tp_btf/sys_enter")
 __success
@@ -240,9 +240,9 @@ int anything_to_untrusted(void *ctx)
 	/* scalar to untrusted */
 	subprog_untrusted(0);
 	/* variable offset to untrusted (map) */
-	subprog_untrusted((void *)mem + off);
+	subprog_untrusted((void *)mem + offset);
 	/* variable offset to untrusted (trusted) */
-	subprog_untrusted((void *)bpf_get_current_task_btf() + off);
+	subprog_untrusted((void *)bpf_get_current_task_btf() + offset);
 	return 0;
 }
 
@@ -298,12 +298,12 @@ int anything_to_untrusted_mem(void *ctx)
 	/* scalar to untrusted mem */
 	subprog_void_untrusted(0);
 	/* variable offset to untrusted mem (map) */
-	subprog_void_untrusted((void *)mem + off);
+	subprog_void_untrusted((void *)mem + offset);
 	/* variable offset to untrusted mem (trusted) */
-	subprog_void_untrusted(bpf_get_current_task_btf() + off);
+	subprog_void_untrusted(bpf_get_current_task_btf() + offset);
 	/* variable offset to untrusted char/enum (map) */
-	subprog_char_untrusted(mem + off);
-	subprog_enum_untrusted((void *)mem + off);
+	subprog_char_untrusted(mem + offset);
+	subprog_enum_untrusted((void *)mem + offset);
 	return 0;
 }