svc_rpcsec_gss.c: Separate out the non-vnet initialization

Without this patch, a single initialization function was
used to initialize both the vnet'd and non-vnet'd data.
This patch separates out the non-vnet'd initializations
into a separate function invoked by SYSINIT().
This avoids use of IS_DEFAULT_VNET() in the initialization
functions and also configures the non-vnet'd initialization
function to be called first, although ordering is not
currently needed.

(cherry picked from commit 57ff348804f98d956f2e203b665de5a8989dbf8c)