devlink: Add a tracepoint for trap reports

Add a tracepoint for trap reports so that drop monitor could register
its probe on it. Use trace_devlink_trap_report_enabled() to avoid
wasting cycles setting the trap metadata if the tracepoint is not
enabled.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>