Bluetooth: BREDR: L2CAP: Recover ident when conn is pending

The `ident` of L2CAP BR connection req will be cleared if
function l2cap_br_conn_req_reply called to send L2CAP BR
connection rsp with result `BT_L2CAP_BR_PENDING`.

Then the invalid `ident` (it is zero) will be filled in
the L2CAP BR connection rsp after the ACL connection is
encrypted.

Recover `ident` if the result of the connection rsp is
`BT_L2CAP_BR_PENDING`.

Signed-off-by: Lyle Zhu <lyle.zhu@nxp.com>