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

Being pedantic here:

I have a problem with a symbol called "MAX_FRAME_SIZE" being set to 1500.
1500 is the maximum payload size.

The Maximum frame since includes DA, DA, EtherType, and may contain additional VLAN tags.
It LOOKS like this symbol is being used in the context of payload size.  If so, please change it to MAX_PAYLOAD_SIZE.  But it also looks like it is being used in the case of UDP messages - in which case this is not at all the same thing since the UDP header takes some of the 1500 octets available and if you are wanting UDP messages to not be fragmented, the size must be shorter than 1500.  But fragmentation with UDP is probably not a problem at all with this use case of the control socket and this means you could increase this to 60K