net/isc-dhcp42-server: Mark DEPRECATED

This port is not receiving a patch for CVE-2015-8605

Also, set EXPIRES to coincide with 2016Q2 branch creation.

The 4.2 branch reached End of Life in March 2015. [1]

[1] https://kb.isc.org/article/AA-01259/0/DHCP-4.2.8-Release-Notes.html

MFH: 2016Q1
Security: 05eeb7e9-b987-11e5-83ef-14dae9d210b8
Security: CVE-2015-8605