kernel/pf: Fix a bunch of gcc47 -Waddress warnings.

kernel/pf: Fix a bunch of gcc47 -Waddress warnings.

The REASON_SET() macro is sometimes called with the address of a local
u_short instead of a pointer passed to the macro's caller. In its NULL
check, gcc47 detects that the address can never be NULL and issues a
-Waddress warning which part of -Wall.

To silence it, go via a u_short pointer in the macro. This fix is about
as harmless as the "issue" gcc47 was warning about.

While here, put two "x" parameters in parentheses.