sample/bpf: fix erspan metadata

The commit c69de58b ("net: erspan: use bitfield instead of
mask and offset") changes the erspan header to use bitfield, and
commit d350a823 ("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: ac80c2a1 ("samples/bpf: add erspan v2 sample code")
Fixes: ef88f89c ("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>