lo: Use new KPI to create the first loop interface

[zlei]

Summary

While here remove a pointless assignment to static local variable lo_cloner.

No functional change intended.

MFC after: 1 week

[zlei]

sys/net/if_loop.c

126

if_alloc() never fail since 4787572d0580 .

[kp]

I was initially worried that we'd change the behaviour of V_loif here, in that it'd get updated every time we create a new loopback interface, but I was wrong. We only set V_loif (although now via ifc_create_ifp() indirectly, rather that from lo_clone_create()) for the first, automatically created, interface.

[zlei]

In D45728#1042970, @kp wrote:

I was initially worried that we'd change the behaviour of V_loif here, in that it'd get updated every time we create a new loopback interface, but I was wrong. We only set V_loif (although now via ifc_create_ifp() indirectly, rather that from lo_clone_create()) for the first, automatically created, interface.

lo: Use new KPI to create the first loop interface

Emm, I think the word assign is more accurate than create.