BUG/MINOR: listener: fix resume_listener() resume return value handling

BUG/MINOR: listener: fix resume_listener() resume return value handling

In resume_listener(), proto->resume() errors were not properly handled:
the function kept flowing down as if no errors were detected.

Instead, we're performing an early return when such errors are detected to
prevent undefined behaviors.

This could be backported up to 2.4.

--
Backport notes:

This commit depends on:
 - "MINOR: listener: make sure we don't pause/resume bypassed listeners"

-> 2.4 ... 2.7:

Replace this:

    |        if (l->bind_conf->maxconn && l->nbconn >= l->bind_conf->maxconn) {
    |                l->rx.proto->disable(l);

By this:

    |        if (l->maxconn && l->nbconn >= l->maxconn) {
    |                l->rx.proto->disable(l);