L2CAP: LE Link Layer Options API

Add the API for L2CAP channel user to get/set link layer options, such
as connection parameter update, and get role.

Add the corresponding PTS test case for it. The next step is to
determine the command from remote feature.

Test: cert/run --host
Change-Id: I7a4e046bc59619c43f975267fe806b88a96b289d