New port: dns/wrapsrv

DNS SRV record command line wrapper

wrapsrv adds support for connecting to a network service based on DNS SRV
record lookups to commands that do not support the DNS SRV record. wrapsrv
implements the weighted priority client connection algorithm in RFC 2782.
The specified command line will be invoked one or more times with %h and %p
sequences in the command line substituted for the hostname and port elements
of the selected SRV record.

WWW: https://github.com/farsightsec/wrapsrv

Differential Revision: https://reviews.freebsd.org/D1488
Approved by: mat (mentor)
Sponsored by: Farsight Security, Inc.