tree-wide: fix 'lenght' typo in comments and code

Some misspelled occurences of 'octet' and some comments were also fixed
as I was on it.

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Cc: Jiri Kosina <trivial@kernel.org>
Cc: Joe Perches <joe@perches.com>
Cc: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>