Add CVE-2018-16301 to CHANGES. [skip ci]

Add CVE-2018-16301 to CHANGES. [skip ci]

One of the effects of commit faf8fb7 was fixing a buffer overflow that
was discovered and reported by Include Security (case reference "F2").
Their work was sponsored by Mozilla under the Secure Open Source
program.  The vulnerability was assigned CVE-2018-16301 on 2018-09-01
(MITRE request reference "scr562827"), but was not properly documented
afterwards.  Add a line to the change log section for 4.99.0, which at
the time of this writing is the first release to incorporate the fix.

See also https://github.com/the-tcpdump-group/libpcap/issues/855