Remove redundant connection_t::status.active field.

Remove redundant connection_t::status.active field.

The only places where connection_t::status.active is modified is in
ack_h() and terminate_connection(). In both cases, connection_t::edge
is added and removed at the same time, and that's the only places
connection_t::edge is set. Therefore, the following is true at all
times:

    !c->status.active == !c->edge

This commit removes the redundant state information by getting rid of
connection_t::status.active, and using connection_t::edge instead.