[media] DocBook media: update STREAMON/OFF documentation

    <para>The <constant>VIDIOC_STREAMON</constant> and

<constant>VIDIOC_STREAMOFF</constant> ioctl start and stop the capture

or output process during streaming (<link linkend="mmap">memory

mapping</link> or <link linkend="userp">user pointer</link>) I/O.</para>

mapping</link>, <link linkend="userp">user pointer</link> or

<link linkend="dmabuf">DMABUF</link>) I/O.</para>

    <para>Specifically the capture hardware is disabled and no input

    <para>Capture hardware is disabled and no input

buffers are filled (if there are any empty buffers in the incoming

queue) until <constant>VIDIOC_STREAMON</constant> has been called.

Accordingly the output hardware is disabled, no video signal is

Output hardware is disabled and no video signal is

produced until <constant>VIDIOC_STREAMON</constant> has been called.

The ioctl will succeed when at least one output buffer is in the

incoming queue.</para>

    <para>Memory-to-memory devices will not start until

<constant>VIDIOC_STREAMON</constant> has been called for both the capture

and output stream types.</para>

    <para>If <constant>VIDIOC_STREAMON</constant> fails then any already

queued buffers will remain queued.</para>

    <para>The <constant>VIDIOC_STREAMOFF</constant> ioctl, apart of

aborting or finishing any DMA in progress, unlocks any user pointer

buffers locked in physical memory, and it removes all buffers from the

not transmitted yet. I/O returns to the same state as after calling

&VIDIOC-REQBUFS; and can be restarted accordingly.</para>

    <para>If buffers have been queued with &VIDIOC-QBUF; and

<constant>VIDIOC_STREAMOFF</constant> is called without ever having

called <constant>VIDIOC_STREAMON</constant>, then those queued buffers

will also be removed from the incoming queue and all are returned to the

same state as after calling &VIDIOC-REQBUFS; and can be restarted

accordingly.</para>

    <para>Both ioctls take a pointer to an integer, the desired buffer or

stream type. This is the same as &v4l2-requestbuffers;

<structfield>type</structfield>.</para>

    <para>If <constant>VIDIOC_STREAMON</constant> is called when streaming

is already in progress, or if <constant>VIDIOC_STREAMOFF</constant> is called

when streaming is already stopped, then the ioctl does nothing and 0 is

returned.</para>

when streaming is already stopped, then 0 is returned. Nothing happens in the

case of <constant>VIDIOC_STREAMON</constant>, but <constant>VIDIOC_STREAMOFF</constant>

will return queued buffers to their starting state as mentioned above.</para>

    <para>Note that applications can be preempted for unknown periods right

before or after the <constant>VIDIOC_STREAMON</constant> or