nimble/mesh: Add bt_mesh_register_gatt to pkg init
nimble/mesh: Add bt_mesh_register_gatt to pkg init

Whenever mesh is initialized we need to make sure gatt services are
registered for GATT proxy

apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble