Commit e6f290535c added libzpool to
the mount_zfs dependencies. This brought in the nvpair symbols
which are used by libzpool. To resolve this include the libnvpair
library for mount_zfs even though mount_zfs doesn't directly
require any of these symbols.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#926