gnutls: upgraded package to upstream

Upgraded net-libs/gnutls to version 3.6.15 on amd64, arm, arm64

BUG=chromium:1128343
TEST=CQ passes

Change-Id: Ib64c2d793ec9ffbb3d2cf9227a2202a5059cb5c8
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/portage-stable/+/2409749
Reviewed-by: Sergei Datsenko <dats@chromium.org>
Reviewed-by: Josh Simmons <simmonsjosh@google.com>
Commit-Queue: Anand K Mistry <amistry@chromium.org>
Tested-by: Anand K Mistry <amistry@chromium.org>
5 files changed