[SetupWizard] Setup Wizard crash on scrolling the list in Select Wi-Fi

screen

 - Setupwizard was crashing because RecyclerView during keyboard scrolls
   invokes onCreateViewHolder(ViewGroup, int) for header view more than
   once. We return the same headerView object each time which causes
   problems later on.
 - Fixed the problem by wrapping the header in a framelayout and
   inserting the header to the current framelayout in
   onBindViewHeader(ViewHolder, int).

Testing:
-------
 - Verified by running on Pixel C, no crashes observed
 - Also attempted scrolling using touchscreen, works as usual.
bug:30789424
Change-Id: I89ac09e14f21ceec3628f249f2cd2a391f020072