RTDM: More IOCTL requests to be handled in primary mode

Xenomai 2 to 3 migration says "RTDM drivers implementing differentiated ioctl() support for both domains should serve all real-time only requests from ioctl_rt(), returning -ENOSYS for any unrecognized request, which will cause the adaptive switch to take place automatically to the ioctl_nrt() handler. The ioctl_nrt() should then implement all requests which may be valid from the regular Linux domain exclusively."

Cosmetic change : rtdm_in_rt_context instead of ipipe_root_p.

Xenomai won't merge .nrt ops delegation to rtdm task through rtpc. Moved it to rtdmnet.c.