qcacld-3.0: Enable/disable roaming based on active NDP sessions

Currently, active NDP sessions are tracked on the platforms
where NAN concurrency handling is supported by host through policy
mgr. Roaming is disabled when an active NDP session is present and
re-enabled when the last NDP session is teardown. But this tracking
is not supported on legacy platforms(which don't advertise either
WMI_SERVICE_NDI_DBS_SUPPORT or WMI_SERVICE_NAN_DISABLE_SUPPORT) as
policy mgr based tracking is not available.
So, disable roaming when the first NDP connection happens and
re-enable when the last peer is departed from HDD APIs in such
legacy platforms.

Change-Id: I6309af12eab9222dc34a79566f7830b7763826de
CRs-Fixed: 2846541