netloop: updates for NetLoop

Fix some issues introduced from commit:
2f70c49e
suggested by Mike Frysinger.

- added some comment for the env_id variable in common_cmd_nvedit.c
- moved some variables in fn scope instead of file scope
- NetInitLoop now static void

Signed-off-by: Heiko Schocher <hs@denx.de>
Acked-by: Ben Warren <biggerbadderben@gmail.com>