Solution: You can add x-cq-linkchecker="valid" parameter in the <a> tag to make sure that links are always mark as valid by CQ. In this case link checker will check the link but will mark it valid.
You can optionally use x-cq-linkchecker="skip" in the <a> as well. In this case link checker will not even check for validity for link.
There are other options too to make all external link as valid,
Option 2: You can disable external link checker entirely by going to felix console
Option 3: Additionally you can add override pattern to disable link checking for certain domain
Example for override pattern: for http://www.day.com you will write ^http://www\.day\.com/
Following error with respect to external link checker,
com.day.cq.rewriter.linkchecker.impl.LinkInfoStorageImpl No more external links allowed for host <Host Name> Maximum of 128 reached. means,
External link checker only checks first 128 link per host basis, And you can find those entry under /var/linkchecker/<protocol>. Unfortunately this is not configurable yet.