sync with latest net-next bpf headers (#2001)

Sync compat bpf.h and virtual_bpf.h with latest net-next versions

Also add a barrier for the test_brb bpf program like below
         meta.prog_id = skb->cb[0];
+        asm volatile("" ::: "memory");
         meta.rx_port_id = skb->cb[1];
so two cb read does not become a 8 byte load which is not
allowed for ubuntu 16.04 kernel (4.4 based). The 8 byte load
is allowed for skb->cb's for later kernels.

Signed-off-by: Yonghong Song <yhs@fb.com>