int prefix_ioctl(gld_mac_info_t *macinfo, queue_t *q, mblk_t *mp);
gldm_ioctl() implements any device-specific ioctl commands. This element is allowed to be null if the driver does not implement any ioctl functions. The driver is responsible for converting the message block into an ioctl reply message and calling the qreply(9F) function before returning GLD_SUCCESS. This function should always return GLD_SUCCESS. The driver should report any errors as needed in a message to be passed to qreply(9F). If the gldm_ioctl element is specified as NULL, GLDv2 returns a message of type M_IOCNAK with an error of EINVAL.