sample/bpf: fix erspan metadata

sample/bpf: fix erspan metadata

The commit dbaf03ad2690 ("net: erspan: use bitfield instead of
mask and offset") changes the erspan header to use bitfield, and
commit 2133ebfc987f ("net: erspan: create erspan metadata uapi header")
creates a uapi header file.  The above two commit breaks the current
erspan test.  This patch fixes it by adapting the above two changes.

Fixes: b9f6dfff10ca ("samples/bpf: add erspan v2 sample code")
Fixes: 0e79372b6a94 ("samples/bpf: extend test_tunnel_bpf.sh with ERSPAN")
Signed-off-by: William Tu <u9012063@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>