Properly add parens around the macro argument. This is not needed by
the kernel but the macro is exported to userspace, so it shouldn't
make any assumptions.

Also use NF_VERDICT_BITS instead of NF_VERDICT_QBTIS for the left-shift
since thats whats logically correct.
Signed-off-by: NPatrick McHardy <kaber@trash.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>