checkpatch, SubmittingPatches: suggest line wrapping commit messages at 75 columns

checkpatch, SubmittingPatches: suggest line wrapping commit messages at 75 columns

Commit messages lines are sometimes overly long.

Suggest line wrapping at 75 columns so the default git commit log
indentation of 4 plus the commit message text still fits on an 80 column
screen.

Add a checkpatch test for long commit messages lines too.

Signed-off-by: Joe Perches <[email protected]>
Cc: David Miller <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Ian Morris <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>