In commit bf4fb51f44, "net: if: Add NET_IF_UP flag"
a reference to ctxt->iface was added in the ipsp_disconnected function.
Let's add the ctxt variable definition to fix the build break.
Change-Id: Ib06047e333504f3db4fe175fb3ef1dce347e1916
Signed-off-by: Michael Scott <michael.scott@linaro.org>