Bluetooth: HFP HF: Handle +CIEV reponse

The +CIEV reponse received from the AG is handle and value is
updated to the application.

> ACL Data RX: Handle 256 flags 0x02 dlen 22         [hci0] 114.667753
      Channel: 64 len 18 [PSM 3 mode 0] {chan 0}
      RFCOMM: Unnumbered Info with Header Check (UIH) (0xef)
         Address: 0x0b cr 1 dlci 0x02
         Control: 0xef poll/final 0
         Length: 14
         FCS: 0x9a
        0d 0a 2b 43 49 45 56 3a 20 32 2c 30 0d 0a 9a     ..+CIEV: 2,0...

Change-Id: I771cdb422d201293d356151fa33ec485083b2356
Signed-off-by: Sathish Narasimman <sathish.narasimman@intel.com>