Due to 6f81927c PJSIP_SC_BUSY_HERE is sent
instead of PJSIP_SC_DECLINE. This means that the signal received must be
taken into account for closing other subcalls on a multi-device context.
Change-Id: Iad36d2a5b07eb75d89a31a5476c6aa5ddeec2ced
GitLab: #547