mi: When {en,dis}abling extensions, match names case-insensitively

Both because extension names are inconsistently capitalized on the wire,
and because the table we're walking spells it COMPOSITE not Composite.
The latter is certainly also a bug, but there's no reason for us to be
that strict.

Signed-off-by: Adam Jackson <ajax@redhat.com>
(cherry picked from commit bf991a5f)