devlink: Add alias "counters_enabled" for "counters" option

To be consistent with netlink attribute name and also with the
"dpipe table show" output, add "counters_enabled" for "counters" in
"dpipe table set" command.

Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>