samples/bpf: xdp_monitor, accept short options

Updated optstring parameter for getopt_long() to accept short options.
Also updated usage() function.

Signed-off-by: Prashant Bhole <[email protected]>
Acked-by: Jesper Dangaard Brouer <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>
1 file changed