BUG/MINOR: config: don't over-count the global maxsock value

BUG/MINOR: config: don't over-count the global maxsock value

global.maxsock used to be augmented by the frontend's maxconn value
for each frontend listener, which is absurd when there are many
listeners in a frontend because the frontend's maxconn fixes an
upper limit to how many connections will be accepted on all of its
listeners anyway. What is needed instead is to add one to count the
listening socket.

In addition, the CLI's and peers' value was incremented twice, the
first time when creating the listener and the second time in the
main init code.

Let's now make sure we only increment global.maxsock by the required
amount of sockets. This means not adding maxconn for each listener,
and relying on the global values when they are correct.