libcoap: remove fix build error on big endian systems

libcoap: remove fix build error on big endian systems

In the big endian case an additional typedef is added in a wrong
position in TinyDTLS. This breaks compiling this code on big endian
systems.

Change-Id: Iad854aba112ddb23bf490b064ec6fbf5d01ce6b6
Signed-off-by: Hauke Mehrtens <hauke.mehrtens@lantiq.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/3951
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: jihwan seo <jihwan.seo@samsung.com>
Reviewed-by: Jon A. Cruz <jonc@osg.samsung.com>