Add client-side support for TLS_FALLBACK_SCSV.

Change-Id: I56626b12407f19e7ed48a680b596e2b2c7b46de1
(cherry picked from commit cc2cd4790cd85023341988efac0ec88b9f630f73)
(cherry picked from commit 13ea96e0f7b06b96689e05142ea0cd9bd2083f45)