In any pool without the extensible dataset feature flag already enabled,
creating a dataset with dedup set to use one of the new checksums would result
in the following panic as soon as any data was added:
panic[cpu0]/thread=ffffff0006761c40: feature_get_refcount(spa, feature,
&refcount) != 48 (0x30 != 0x30), file: ../../common/fs/zfs/zfeature.c line 390

ffffff0006761830 fffffffffba8fbdd ()
ffffff0006761890 zfs:feature_do_action+11a ()
ffffff00067618c0 zfs:spa_feature_incr+1e ()
ffffff0006761920 zfs:dmu_object_zapify+b7 ()
ffffff00067619b0 zfs:dsl_dataset_activate_feature+97 ()
ffffff0006761a20 zfs:dsl_dataset_sync+ba ()
ffffff0006761ab0 zfs:dsl_pool_sync+153 ()
ffffff0006761b70 zfs:spa_sync+26e ()
ffffff0006761c20 zfs:txg_sync_thread+227 ()
ffffff0006761c30 unix:thread_start+8 ()
Inspection showed that feature->fi_feature was 7, which is the value of
SPA_FEATURE_EXTENSIBLE_DATASET in the spa_feature enum.
Testing shows that the panic can be prevented by explicitly setting extensible
dataset as a dependency for the sha512, edonr, and skein feature flags.
Alternatively, the new checksums code could possibly be changed to obviate the
need for the dependency.