mon: Deny EC optimizations (fast EC) for non-4k-aligned chunk-sizes.

mon: Deny EC optimizations (fast EC) for non-4k-aligned chunk-sizes.

There are some bugs in the way Fast EC handles non 4k-aligned chunk sizes.

Such chunk sizes are buggy and even if they did work, the performance
would not be very good.  Storage efficiency is also not helped by these
unusual encodings.

This commit will reject any attempt to turn optimizations (fast EC) on.

If the default is set to turn optimizations on, then this will be ignored
if the profile is not 4k aligned.

Note that to create a profile in the first place requires a --force override.

Signed-off-by: Alex Ainscow <aainscow@uk.ibm.com>