security/bro: Update to 2.5.3 and address security advisory

[leres]

Summary

Proposed commit message:

Update to 2.5.3 which fixes an integer overflow:

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

Note that a CVE has not been assigned yet.

Reviewed by: ? (mentor)
Approved by: ? (mentor)
MFH: 2018Q1
Security: 044cff62-ed8b-4e72-b102-18a7d58a669f
Differential Revision: ?

[matthew]