Fix issues revealed by -Wextra flag.

Fix issues revealed by -Wextra flag.

Fix assorted warnings raised by the -Wextra flag, including
a few significant items. Reduced local build warnings from
over 9200 warnings to about 650.

At least one unicast send routine would drop all errors due
to type issues.

Change-Id: I9d8c90f83ccc89d9fba809f303ccf42b96c0eb82
Signed-off-by: Jon A. Cruz <jonc@osg.samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/2018
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Erich Keane <erich.keane@intel.com>