tc: Fix for missing estimator initialization

tc: Fix for missing estimator initialization

When switching to C99 initializers, I forgot to add this one. This means
that when trying to set an estimator value, tc would complain about
spurious duplicate estimator parameter. But much worse, the random
variable content is sent to the kernel regardless of whether an
estimator was given or not.

Fixes: d17b136f7d7dd ("Use C99 style initializers everywhere")
Reported-by: Stas Nichiporovich <stasn77@gmail.com>
Signed-off-by: Phil Sutter <phil@nwl.cc>