ble_gatts_notify_multiple_custom() function

Sends a "free-form" multiple handle variable length characteristic notification. This function consumes supplied mbufs regardless of the outcome. Notifications are sent in order of supplied entries. Function tries to send minimum amount of PDUs. If PDU can't contain all of the characteristic values, multiple notifications are sent. If only one handle-value pair fits into PDU, or only one characteristic remains in the list, regular characteristic notification is sent. If GATT client doesn't support receiving multiple handle notifications, this will use GATT notification for each characteristic, separately. If value of characteristic is not specified it will be read from local GATT database.