invoke bta_av_sco_chg_cback when SCO goes from SHUTTING to SHUTDOWN state

When BTA_AG_SCO_OPEN_ST transits to BTA_AG_SCO_SHUTTING_ST, the bta_av_sco_chg_cback may not report # of sco links on time.
Add another bta_av_sco_chg_cback check when BTA_AG_SCO_SHUTTING_ST goes to BTA_AG_SCO_SHUTDOWN_ST.

Bug: 234976097
Change-Id: I2e370facd0e01054645d018a663e41e2401a1f0f
Test: manual