SM: Implement an attempt to upgrade the link security

When an profile/application registers with L2CAP it will define
a required security level.  L2CAP will call in to enforce the level
and we will attempt to achieve this level if we have not already
obtained the level of security required.

Bug: 145638034
Test: cert/run --host --test_filter=SecurityTest
Tag: #gd-refactor
Change-Id: I895fe2722bd74460ab5bd52e37bc0e9cbb9b4c0f