s4-common: remove unused overlay options

Change-Id: I618d374a4fb9417637b90b4e25a292adbec11748
s4-common: move network config to s4-common

Change-Id: I25d02cd3f382ed423c4d45ea3a566bf4e8c9e25a
s4-common: use bt-pan for BT tether

Change-Id: I7a1a54096b7d1a782a8d872e37d9d39da9d24fee