taskprocessor.c: Increase the number of tps_singletons container buckets.

Since v12 the number of taskprocessors in the system has increased a lot.
Small systems can easily have over a hundred and larger systems can have
thousands.

Most uses of the tps_singletons container deal with creating and
destroying the taskprocessors.  However, the pjsip distributor looks up
taskprocessors/serializers by name frequently.  It needs to find the
serializer for incoming SIP responses to distribute them to the
appropriate serializer.

Change-Id: Ice0603606614ba49f7c0c316c524735c064e7e43