samples/bpf: fix bpf tunnel cleanup

test_tunnel_bpf.sh fails to remove the vxlan11 tunnel device, causing the
next geneve tunnelling test case fails.  In addition, the geneve reserved bit
in tcbpf2_kern.c should be zero, according to the RFC.

Signed-off-by: William Tu <u9012063@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>