BTA_AvMetaCmd() function

* Function BTA_AvMetaCmd * Description Send a Metadata/Advanced Control command. The message contained * in p_pkt can be composed with AVRC utility functions. * This function can only be used if AV is enabled with feature * BTA_AV_FEAT_METADATA. * This message is sent only when the peer supports the TG role. 8 The only command makes sense right now is the absolute volume command. * Returns void