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>