Increase RFC_MCB_RELEASE_INACT_TIMER to 20 seconds

Say we first connect to a remote device using RFCOMM.  The remote
decides to bond with us before we establish a channel.  This could take
longer than 2 seconds.

In the past we handle this before we create L2cap channel.  However,
re-bond can happen during RFCOMM session, because security requirement
might have changed.

Test: cert/run
Tag: #gd-refactor
Bug: 141555841
Change-Id: I7d5618b37d5414b10abe7497c3ea6819fb802db7