[bt][data] SocketChannelRelay: remove a template argument

Instead of having SocketChannelRelay provide the channel's identifier
to the SocketFactory when invoking the DeactivationCallback, have the
factory capture the identifier into the callback. This eliminates the
need for the SocketChannelRelay to know about ChannelIdT.

Bug: NET-1932
Test: bt-host-unittests (on eve)
Change-Id: I9ef4505a1828ced9653849114e5d2e6a3517fd7d
9 files changed