docs: update patch size in SubmittingPatches

This patch size comment is like so last millenium.  Update it to modern
times.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/SubmittingPatches

@@ -232,7 +232,7 @@ your e-mail client so that it sends your patches untouched.
 When sending patches to Linus, always follow step #7.
 
 Large changes are not appropriate for mailing lists, and some
-maintainers.  If your patch, uncompressed, exceeds 40 kB in size,
+maintainers.  If your patch, uncompressed, exceeds 300 kB in size,
 it is preferred that you store your patch on an Internet-accessible
 server, and provide instead a URL (link) pointing to your patch.