bond: remove debug function to fix link with shared lib

bond: remove debug function to fix link with shared lib

The function print_client_stats was used in the example without being
clearly exported in the map file. So it breaks linking with shared library
when debug is enabled.
It's better to remove this function as it probably could be implemented
with statistics API.

Fixes: cc7e8ae84faa ("add example application for link bonding mode 6")

Signed-off-by: Thomas Monjalon <thomas.monjalon@6wind.com>
Acked-by: Declan Doherty <declan.doherty@intel.com>