When debugging is enabled on a very recent version of gcc
(tested with 5.3.0), DVA_SET_GANG(dva, !!(flags)) fails
because an assertion causes a comparison between what is
technically a boolean and an integer.
Signed-off-by: DHE <git@dehacked.net>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#4465