Pre-zero the MAC context.
Pre-zero the MAC context.

Security:	CVE-2013-4548
Security:	FreeBSD-SA-13:14.openssh
Approved by:	re (implicit)

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase