Bluetooth: RFCOMM: Initiate session connection

This patch introduces the Connect API which initiates session
connection first. If session is already there with the peer
then it has to reuse it and initiate DLC (which will be done
in the subsequent patch) since there can be only one session
per device.

< ACL Data TX: Handle 256 flags 0x00 dlen 8
      Channel: 64 len 4 [PSM 3 mode 0] {chan 0}
      RFCOMM: Set Async Balance Mode (SABM) (0x2f)
         Address: 0x03 cr 1 dlci 0x00
         Control: 0x3f poll/final 1
         Length: 0
         FCS: 0x1c

> ACL Data RX: Handle 256 flags 0x02 dlen 8
      Channel: 64 len 4 [PSM 3 mode 0] {chan 0}
      RFCOMM: Unnumbered Ack (UA) (0x63)
         Address: 0x03 cr 1 dlci 0x00
         Control: 0x73 poll/final 1
         Length: 0
         FCS: 0xd7

Change-Id: I9828e0f3b3ea43bb17df95f0536e15df86f1b4be
Signed-off-by: Jaganath Kanakkassery <jaganathx.kanakkassery@intel.com>