Remove ability to override netns

This gives a lot of operational problems later. It's definitely reasonable
to be able to create tap interfaces in other namespaces, and this is
still possible (see below for syntax).

However, changing the runtime netns makes the netlink listener much more
complicated because it will have to listen on not just one netns, but all
of them, for netlink updates.

So, for now, let's remove the ability to set the namespace in the API.
Still possible:
- set at startup.conf in lcpng { netns <x> }
- force creating in 'lcpng create ... netns <x>'

This will nudge folks to create one singular namespace (say,
'dataplane', in the startup.conf), and then handle all netlink messages
in that namespace only.

lcpng_if.api

@@ -21,34 +21,34 @@ option version = "1.0.0";
 
 import "vnet/interface_types.api";
 
-/** \brief Set the default Linux Control Plane namespace
+/** \brief Set the namespace for Linux Control Plane host taps
     @param client_index - opaque cookie to identify the sender
     @param context - sender context, to match reply w/ request
-    @param namespace - the new default namespace; namespace[0] == 0 iff none
+    @param namespace - the new namespace; namespace[0] == 0 iff none
 */
-autoreply define lcp_default_ns_set
+autoreply define lcp_netns_set
 {
   u32 client_index;
   u32 context;
   string namespace[32];		/* LCP_NS_LEN */
 };
 
-/** \brief get the default Linux Control Plane namespace
+/** \brief get the Linux Control Plane namespace
     @param client_index - opaque cookie to identify the sender
     @param context - sender context, to match reply w/ request
 */
-define lcp_default_ns_get
+define lcp_netns_get
 {
   u32 client_index;
   u32 context;
 };
 
-/** \brief get the default Linux Control Plane namespace
+/** \brief get the Linux Control Plane namespace
     @param client_index - opaque cookie to identify the sender
     @param context - sender context, to match reply w/ request
-    @param namespace - the default namespace; namespace[0] == 0 iff none
+    @param namespace - the namespace; namespace[0] == 0 iff none
 */
-define lcp_default_ns_get_reply
+define lcp_netns_get_reply
 {
   u32 context;
   string namespace[32];		/* LCP_NS_LEN */