Merge branch 'gtp-sgsn-side-tunnel'

Jonas Bonn says:

====================
GTP SGSN-side tunnel

Changes since v4:

* Respin the series on top of net-next; the conflicts were trivial,
  amounting to just code having been shifted about
====================

Signed-off-by: David S. Miller <davem@davemloft.net>