Add PASSDROP_OPCODE test, ensuring counter increment

This commit introduces new testcases for PASSDROP_OPCODE. The test
verifies that the packet is passed/dropped and the counter is
incremented correctly when this opcode is executed.

This commit also contains some minor stylistic changes.

Test: TH
Change-Id: I3f84e7e5a9f9846cd67e8298a7bd1e07adddc846