switch from SEC() to DEFINE_BPF_PROG()

I keep on failing to find this using grep because it
doesn't match how all the other programs are defined,
so change it for consistency.

Test: builds, atest, TreeHugger
Signed-off-by: Maciej <Żenczykowski&lt;maze@google.com>
Change-Id: Ifc9acc877d6fcf2b5843e8a9370cea99ab6cc551