MFC r260039:

Turn off warnings about unused variables for a bunch of files under
contrib/ipfilter.
MFC r260046 (by glebius):

Fix the parse type for NGM_LISTTYPES.

Actually, text versions of generic commands are not used, since ngctl(8)
uses binary messages for them. And to request a text command one needs
a working ngctl(8). That's why the bug was never discovered. I'm pondering
on removing the text support for generic commands.

Found by:	dim with clang 3.4