Report MMP_STATE_NO_HOSTID immediately

Report MMP_STATE_NO_HOSTID immediately

There is no need to perform the activity check before detecting that the
user must set the system hostid, because the pool's multihost property
is on, but spa_get_hostid() returned 0.  The initial call to
vdev_uberblock_load() provided the information required.

Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Closes #6388