Fixed issue to pass PSK identity hint to application in callback

Fixed issue to pass PSK identity hint to application in callback

In cases (with PSK ciphersuite) where Server is sending
'PSK Identity Hint’ inside ServerKeyExchange message, DTLS library
is not passing the ‘identity hint’ inside ‘desc’ argument in
get_psk_info(DTLS_PSK_KEY, desc) callback. Instead, ‘desc’ contains
the identity of the client itself. The reason for this is that the
code inside dtls_send_client_key_exchange() method
overwrites the ‘identity hint’ received earlier.

Change-Id: Ibf447e3a6b33284118908a52aed4cf636038ab23
Signed-off-by: Sachin Agrawal <sachin.agrawal@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/119
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Sakthivel Samidurai <sakthivel.samidurai@intel.com>
Reviewed-by: Sashi Penta <sashi.kumar.penta@intel.com>
Reviewed-by: Sudarshan Prasad <sudarshan.prasad@intel.com>
(cherry picked from commit 72a92249258601e2ab799628733afcb7c4c9b1e9)
Reviewed-on: https://gerrit.iotivity.org/gerrit/310