We are not setting the 'always rendezvous for mca' flag.  kdb needs it
set to get decent mca debugging on all cpus but I do not want kdb to
change sal behaviour.  Since we do not recover from mca without a
debugger, I see no reason why this flag should not be on for all
kernels.

The rendezvous timeout was set to 100 * HZ, but SAL expects the timeout
to be in milliseconds, HZ may not be 1 millisecond.  The patch makes
the timeout an explicit 20 seconds, semi-arbitrary value.