So allocating the object fails, returning B_NO_MEMORY.

Probably because the heap hasn't been initialised yet,
so doing so in efi/start.cpp isn't effective. Perhaps
it should be moved to main.cpp?
Use a static instance of NetStack; we can't allocate objects
on the heap just yet... ironically, the whole setup currently
uses a singleton pattern anyway, so should clean this up to
do it without needing to allocate on the heap.