monitor: Fix selecting PSM for L2CAP frame
monitor: Fix selecting PSM for L2CAP frame

Current code could fail to pick up right PSM resulting in using PSM 1
for non-SDP traffic.

Fix following:
> ACL Data RX: Handle 3 flags 0x02 dlen 9
    Channel: 64 len 5 [PSM 1 mode 0] {chan 0}
      invalid frame size
> ACL Data RX: Handle 3 flags 0x02 dlen 20
    Channel: 64 len 16 [PSM 1 mode 0] {chan 0}
      invalid frame size
      2b 42 52 53 46 3d 32 35 35 0d e4                 +BRSF=255..
< ACL Data TX: Handle 3 flags 0x00 dlen 28
    Channel: 256 len 24 [PSM 3 mode 0] {chan 1}
    RFCOMM: Unnumbered Info with Header Check (UIH)(0xef)
       Address: 0x69 cr 0 dlci 0x1a
       Control: 0xef poll/final 0
       Length: 20
       FCS: 0x3e
      0d 0a 2b 42 52 53 46 3a 20 38 37 31 0d 0a 0d 0a  ..+BRSF: 871....
      4f 4b 0d 0a 3e                                   OK..>

instead of:
> ACL Data RX: Handle 4 flags 0x02 dlen 20
    Channel: 64 len 16 [PSM 3 mode 0] {chan 1}
    RFCOMM: Unnumbered Info with Header Check (UIH)(0xef)
       Address: 0x6b cr 1 dlci 0x1a
       Control: 0xef poll/final 0
       Length: 12
       FCS: 0xe4
      41 54 2b 42 52 53 46 3d 32 35 35 0d e4           AT+BRSF=255..
< ACL Data TX: Handle 4 flags 0x00 dlen 28
    Channel: 384 len 24 [PSM 3 mode 0] {chan 1}
    RFCOMM: Unnumbered Info with Header Check (UIH)(0xef)
       Address: 0x69 cr 0 dlci 0x1a
       Control: 0xef poll/final 0
       Length: 20
       FCS: 0x3e
      0d 0a 2b 42 52 53 46 3a 20 38 37 31 0d 0a 0d 0a  ..+BRSF: 871....
      4f 4b 0d 0a 3e                                   OK..>

silent-snowman/bluez,mapfau/bluez,ComputeCycles/bluez,mapfau/bluez,pstglia/external-bluetooth-bluez,pkarasev3/bluez,pstglia/external-bluetooth-bluez,silent-snowman/bluez,pkarasev3/bluez,pstglia/external-bluetooth-bluez,pkarasev3/bluez,ComputeCycles/bluez,silent-snowman/bluez,mapfau/bluez,pstglia/external-bluetooth-bluez,ComputeCycles/bluez,ComputeCycles/bluez,mapfau/bluez,silent-snowman/bluez,pkarasev3/bluez