OpenZFS 5778 - nvpair_type_is_array() does not recognize DATA_TYPE_INT8_ARRAY

OpenZFS 5778 - nvpair_type_is_array() does not recognize DATA_TYPE_INT8_ARRAY

Authored by: Andriy Gapon <avg@icyb.net.ua>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Prakash Surya <prakash.surya@delphix.com>
Approved by: Dan McDonald <danmcd@omniti.com>
Reviewed-by: Don Brady <dev.fs.zfs@gmail.com>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Ported-by: Giuseppe Di Natale <dinatale2@llnl.gov>
OpenZFS-issue: https://www.illumos.org/issues/5778
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/bf4d553
Closes #6580