Fix ECDSA signature verification (IOT-793)

Fix ECDSA signature verification (IOT-793)

Earlier Fix was not compatible with external SSL libraries because
the signed ECC point was not in correct format. This change has
been verified to be working with upstream tinyDTLS.
This change has been reviewed at
https://gerrit.iotivity.org/gerrit/#/c/3647/

Change-Id: I2bc4d01f8c1a950f9e6e6ac8eaf200c28060c5dc
Signed-off-by: Sachin Agrawal <sachin.agrawal@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/3737
Reviewed-by: dongik Lee <dongik.lee@samsung.com>
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>