mrpdclient lib use, step 1

I was on my way to convert the talker/listener pairs to use mrpdclient, but in the process introduced two API changes to it.

I converted to this new API the minimum to pass Travis: mrpctl, mrpl, mrpq, mrpValidate.

The 2 important commits are:

mrpdclient API change: application need not to know the mrpd socket port number
https://github.com/jbmaillet/Open-AVB/commit/1201e3b82907254dcf4d4e4a63368008e3d0835e

mrpdclient: API change, un-globify the socket connection to mrpd
https://github.com/jbmaillet/Open-AVB/commit/3be37c4a5390312c3f1ede00d0dcea3501491630

> I hesitate to remove the capability to have two different instances of mrpd running on different Ethernet ports. I know current code does not support this, but in my mind the simplest method would be to add the client port as a command line parameter to mrpd and then have a client attach to both instances of mrpd via differing ports. I know it would not be a "final" multi-port solution, but it would be a good place to start.

Opened issue #161 "multiple mrpd running on different Ethernet ports":

https://github.com/AVnu/Open-AVB/issues/161

(...but I can't label it. Would someone p@lease add the "enhancement" + "MRP" labels?)