Corrected error return value when parsing fragmentation header.

Corrected error return value when parsing fragmentation header.

CAParseHeader() on error returned CA_STATUS_INVALID_PARAM, a
CAResult_t value, instead of a value that matches uint32_t return
type.  Return zero on error instead.

Updated documentation accordingly.

Change-Id: I3dee0e2b562a272c5d41963e0049618d7bacd69e
Signed-off-by: Ossama Othman <ossama.othman@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/1419
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Erich Keane <erich.keane@intel.com>