selftests: bpf: notification about privilege required to run test_lwt_seg6local.sh testing script

This test needs root privilege for it's successful execution.

This patch is atleast used to notify the user about the privilege
the script demands for the  smooth execution of the test.

Signed-off-by: Jeffrin Jose T (Rajagiri SET) <ahiliation@gmail.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>