[bluez] Include held calls in call status indicator

Some carkits get confused by call=0 indicator ofono code sends when an
active call is terminated while there is also a held call present;
They expect the call status indicator to remain at 1 instead.

Strictly speaking HFP 1.5 specifies that call=1 only when there are
active calls, while HFP 1.6 changes the indicator to be 1 when there
are calls in progress (thus having the same meaning as 3GPP 27.007).

In addition, HFP 1.5 figure 4.50 makes no mention of indicating call=0
when releasing an active call while there is a held call present,
which seems to contradict the specification of call status values.

Thus, change code to indicate call=1 also when there are held calls.