docs: ioctl-number.txt: convert it to ReST format

The conversion itself is simple: add a markup for the
title of this file and add markups for both tables.

Yet, the big table here with IOCTL numbers is badly formatted:
on several lines, the "Include File" column has some values that
are bigger than the reserved space there.

Also, on several places, a comment was misplaced at the "Include
File" space.

So, most of the work here is to actually ensure that each field
will be properly fixed.

Also worth to mention that some URLs have the asterisk character
on it. Well, Sphinx has an issue with asterisks in the middle
of an string. As this is URL, use the alternate format: %2A.

As a side effect of this patch, it is now a lot easier to see that
some reserved ioctl numbers are missing the include files
where it is supposed to be used.

PS.: While this is part of a subdir, I opted to convert this
single file alone, as this file has a potential of conflicts,
as most subsystem maintainers touch it.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

include/uapi/rdma/rdma_user_ioctl_cmds.h

@@ -36,7 +36,7 @@
 #include <linux/types.h>
 #include <linux/ioctl.h>
 
-/* Documentation/ioctl/ioctl-number.txt */
+/* Documentation/ioctl/ioctl-number.rst */
 #define RDMA_IOCTL_MAGIC	0x1b
 #define RDMA_VERBS_IOCTL \
 	_IOWR(RDMA_IOCTL_MAGIC, 1, struct ib_uverbs_ioctl_hdr)