restore allowance for tcp-clients < interfaces

restore allowance for tcp-clients < interfaces

in the "refactor tcpquota and pipeline refs" commit, the counting
of active interfaces was tightened in such a way that named could
fail to listen on an interface if there were more interfaces than
tcp-clients. when checking the quota to start accepting on an
interface, if the number of active clients was above zero, then
it was presumed that some other client was able to handle accepting
new connections. this, however, ignored the fact that the current client
could be included in that count, so if the quota was already exceeded
before all the interfaces were listening, some interfaces would never
listen.

we now check whether the current client has been marked active; if so,
then the number of active clients on the interface must be greater
than 1, not 0.

(cherry picked from commit 0b4e2cd4c3192ba88569dd344f542a8cc43742b5)