Prevent race condition in setting up L2CAP

Since outgoing and incoming were accessing the same underlying data
structure, if both were in progress one could overwrite the data
present and the first to succeed would cause the following one to crash.

Instead pass the data directly in the closure, to remove unnecessary
fields and ensure the data is present.

Test: cert/run --host
Tag: #gd-refactor
Bug: 159815595
Change-Id: Ibd7f98ea29d06c0a1b8864fe08adf95572c06ca4