Add tests that exercise public key checks for ECDH

Add tests that exercise public key checks for ECDH

When performing ECDH the peer provided public key needs to be checked
for validity. FIPS requires basic tests be performed to insure the
provided points are in fact on the selected curve. Those checks already
exists in the ecc_point_set() function.
Add an explicit test that checks the boundaries so that any regression
in checks will be caught.

Signed-off-by: Simo Sorce <simo@redhat.com>