[rilmodem] Fix for call waiting status query

As stated on 3GPP 27.007, 7.12 Call waiting +CCWA:
"When querying the status of a network service (<mode>=2) the response
line for 'not active' case (<status>=0) should be returned only if service is
not active for any <class>."
If status is 'active', rilmodem will provide bitmap of service classes having
CW enabled to oFono core. Core will mask from this bitmap, whether CW
is enabled for voice call

Signed-off-by: Petri Takalokastari <petri.takalokastari@oss.tieto.com>