tests/kcmp: add more checks

Let's check all kcmp commands that they indeed do not print idx1/idx2.
Also, check that upper bits of pid arguments are ignored.

* tests/gen_tests.in (kcmp): Decrease -a argument's value from 27 to 22.
* tests/kcmp.c: Add checks for upper bits of pid1/pid2 and for all
kcmp types not tested before.