MFC r277300 (by smh): Mechanically convert cddl sun #ifdef's to illumos

Since the upstream for cddl code is now illumos not sun, mechanically
convert all sun #ifdef's to illumos #ifdef's which have been used in all
newer code for some time.

Also do a manual pass to correct the use if #ifdef comments as per style(9)
as well as few uses of #if defined(__FreeBSD__) vs #ifndef illumos.

MFC r269524:
Preserve the errno value of an ioctl before calling free(3). Previously,
errno was very occasionally being clobbered, resulting in a bogus error from
dt_consume() and thus an error from dtrace(1).

MFC r269524:
Preserve the errno value of an ioctl before calling free(3). Previously,
errno was very occasionally being clobbered, resulting in a bogus error from
dt_consume() and thus an error from dtrace(1).