CTL: Fix mode page trucation on HA synchronization.

Due to variable size of struct ctl_ha_msg_mode ctl_isc_announce_mode()
sent only first 4 bytes of modified mode page to the other HA side,
that caused its corruption there, noticeable only after failover.

I've found alike bug also in ctl_isc_announce_lun(), but there it was
sending slightly more than needed, that is a smaller problem.

MFC after: 1 week
Sponsored by: iXsystems, Inc.

(cherry picked from commit 1a8d8a3a909f906ed69cca080a6446e7295bcbbb)