Add CAP_FCNTL and use cap_fcntls_limit().

Add CAP_FCNTL and use cap_fcntls_limit().

Without these changes pcap_dump_ftell() will return -1 and set errno to
ENOTCAPABLE.

This allows you to do:

tcpdump -C 1 -W 5 -w foo.pcap

Without these changes it will never rotate to foo.pcap1 and continue writing
to foo.pcap0 forever.

Discussed at: http://unix.derkeiler.com/Mailing-Lists/FreeBSD/current/2014-09/msg00142.html