docs/devel/ebpf_rss.rst: Format literals correctly

docs/devel/ebpf_rss.rst: Format literals correctly

In rST markup, single backticks `like this` represent "interpreted
text", which can be handled as a bunch of different things if tagged
with a specific "role":
https://docutils.sourceforge.io/docs/ref/rst/restructuredtext.html#interpreted-text
(the most common one for us is "reference to a URL, which gets
hyperlinked").

The default "role" if none is specified is "title_reference",
intended for references to book or article titles, and it renders
into the HTML as <cite>...</cite> (usually comes out as italics).

To format a literal (generally rendered as fixed-width font),
double-backticks are required.

ebpf_rss.rst gets this wrong in a few places; correct them.

Signed-off-by: Peter Maydell <[email protected]>
Reviewed-by: Richard Henderson <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Message-id: 20210726142338[email protected]