Change ASSERT(!"...") to cmn_err(CE_PANIC, ...)

Change ASSERT(!"...") to  cmn_err(CE_PANIC, ...)

There are a handful of ASSERT(!"...")'s throughout the code base for
cases which should be impossible.  This patch converts them to use
cmn_err(CE_PANIC, ...) to ensure they are always enabled and so that
additional debugging is logged if they were to occur.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #1445