p224_felem_neg does not produce an output within the tight bounds
suitable for p224_felem_contract. This was found by inspection of the
code.
This only affects the final y-coordinate output of arbitrary-point
multiplication, so it is a no-op for ECDH and ECDSA.
Change-Id: I1d929458d1f21d02cd8e745d2f0f7040a6bb0627
Reviewed-on: https://boringssl-review.googlesource.com/26847
Commit-Queue: David Benjamin <davidben@google.com>
Commit-Queue: Adam Langley <agl@google.com>
Reviewed-by: Adam Langley <agl@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>