When this test was written only group 19 was supported. The 'bad_group'
test used, at the time, unsupported group 20. Now group 20 is supported
so this test was expecting a failure. This updates the test to use group
0xff, which is not a valid ECC group and should always fail.
Now that the peer element is validated we must send valid point data.
This should have been done in the beginning anyways, but since the
point data was not previously validated this test still passed.
Since this particular unit test is really testing timeouts we can just
use the commit buffer for other tests since it contains a valid scalar
and point.
