By default, mysqldump generates only one INSERT command per table, resulting in one (very long) line of inserted data for each table that got dumped. This is essentially because the “batch” inserts are much faster than if it generated a separate INSERT query for every record in every table.
So, it’s not that mysqldump has created arbitrarily long lines, and you can just impose some other cutoff length. The lines are long for a reason.
If it’s really important to get the INSERTs broken down onto multiple lines, you can indicate that with:
mysqldump --extended-insert=FALSE --complete-insert=TRUE ...
Note, however, that restoring tables will take longer in this format.