pf tests: Test automatically generated tables

Add a test case where the pfctl optimizer will generate a table
automatically. These tables have long names, which we accidentally broke
in the nvlist ADDRULE ioctl.

Reviewed by: melifaro
MFC after: 2 weeks
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D29989