LE L2cap shim: Implement fixed channel timeout

Implement timeout settings with Fixed channel acquire/release.  So far
we only have two timeout options: no timeout, and disconnect
immediately, which we can use existing methods to implement.

Test: CtsVerifier
Tag: #gd-refactor
Bug: 141555841
Change-Id: If262e2773575b5c3c99a7286d66ca5f6a7fe7e58