Adjust global variables setting

As pointed by Timo (and https://ebpf-go.dev/concepts/global-variables/),
we no longer need to use static, and then use Variables().Set() to
set it (RewriteConstants() is deprecated).

Suggested-by: Timo Beckers <timo@isovalent.com>
Signed-off-by: Martynas Pumputis <m@lambda.lt>

bpf/kprobe_pwru.c

@@ -155,7 +155,7 @@ struct config {
 	u32 shinfo_btf_id;
 } __attribute__((packed));
 
-static volatile const struct config CFG;
+volatile const struct config CFG;
 #define cfg (&CFG)
 
 #define MAX_STACK_DEPTH 50

main.go

@@ -170,9 +170,7 @@ func main() {
 	if err != nil {
 		log.Fatalf("Failed to get pwru config: %v", err)
 	}
-	if err := bpfSpec.RewriteConstants(map[string]interface{}{
-		"CFG": pwruConfig,
-	}); err != nil {
+	if err := bpfSpec.Variables["CFG"].Set(pwruConfig); err != nil {
 		log.Fatalf("Failed to rewrite config: %v", err)
 	}