external/boringssl: add dummy EC_GROUP_set_point_conversion_form.

BoringSSL always uses uncompressed points. This function aborts if
another form is requested or does nothing if uncompressed points are
requested.

Bug: 20419899
Change-Id: Ib5d0707c4e9eaee67e46a0d73d41be70ce0a9353
2 files changed