NSS: add `padding' extension when we might hit the F5 bug.

In the case that a ClientHello record is between 256 and 511 bytes long, add an
extension to make it at least 512 bytes. This works around a bug in F5 terminators.

BUG=315828

Review URL: https://codereview.chromium.org/62103003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234040 0039d316-1c4b-4281-b951-d872f2087c98
7 files changed