libwg-go: more efficient and safer string passing

It was unclear when the Go string was actually freed.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

app/tools/libwg-go/src/git.zx2c4.com/wireguard-go/api-android.go

@@ -161,8 +161,8 @@ func wgGetSocketV6(tunnelHandle int32) int32 {
 }
 
 //export wgVersion
-func wgVersion() string {
-	return WireGuardGoVersion
+func wgVersion() *C.char {
+	return C.CString(WireGuardGoVersion)
 }
 
 func main() {}