Mark bro < 2.5.3 as vulnerable

[leres]

Summary

Proposed commit message:

Mark bro < 2.5.3 as vulnerable as per:

http://blog.bro.org/2018/02/bro-253-released-security-update.html

Reviewed by: ? (mentor)
Approved by: ? (mentor)
Security: ?
Differential Revision: ?

Note that a CVE has not been assigned yet.

[matthew]

[leres]

Another differential that didn't close with the with the commit (r462045).