Fix fasttrap ioctls and headers_check.

Fix fasttrap ioctls and headers_check.

These were being included before their structure definitions, leading to the
possibility of wrong values for FASTTRAPIOC_*.

Instead, split the FASTTRAPIOC* definitions into a new header, fasttrap_ioctl.h:
this includes fasttrap.h to get the structure definitions, and is also included
by it, so that either header can be included to get the ioctl definitions. We
then extend "make headers_check" so that it does the extended ioctl checks on
all headers named *ioctl.h, not just ioctl.h. (These checks are quite grotesque:
we don't want to run them on every DTrace uapi header if that can be avoided.)

Signed-off-by: Nick Alcock <nick.alcock@oracle.com>