docs-rst: conf.py: adjust the size of .. note:: tag

While the current implementation works well when using as a
paragraph, it doesn't work properly if inside a table. As we
have quite a few such cases, fix the logic to take the column
size into account.

PS.: I took the logic there from the latest version of Sphinx.sty
Signed-off-by: NMauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

Documentation/conf.py

@@ -282,7 +282,13 @@ latex_elements = {
         \\definecolor{MyGray}{rgb}{0.80,0.80,0.80}
 
         \\makeatletter\\newenvironment{graybox}{%
-           \\begin{lrbox}{\\@tempboxa}\\begin{minipage}{\\columnwidth}}{\\end{minipage}\\end{lrbox}%
+	   \\newlength{\\py@noticelength}
+	   \\setlength{\\fboxrule}{1pt}
+	   \\setlength{\\fboxsep}{7pt}
+	   \\setlength{\\py@noticelength}{\\linewidth}
+	   \\addtolength{\\py@noticelength}{-2\\fboxsep}
+	   \\addtolength{\\py@noticelength}{-2\\fboxrule}
+           \\begin{lrbox}{\\@tempboxa}\\begin{minipage}{\\py@noticelength}}{\\end{minipage}\\end{lrbox}%
            \\colorbox{MyGray}{\\usebox{\\@tempboxa}}
         }\\makeatother