net/net.c: cosmetic: fix lines over 80 characters

This removes the following checkpatch warning:
 - WARNING: line over 80 characters

There are three such warnings left.

The first is hard to fix with cosmetic-only changes without compromising code
readability, so I'm leaving it as it is for now:
  WARNING: line over 80 characters
  #1537: FILE: net.c:1537:
  + [4 tabs] memcpy(((Ethernet_t *)NetArpWaitTxPacket)->et_dest, ...

The other two cannot be fixed without splitting string literals, so it is
preferred to keep them longer than 80 characters.

Signed-off-by: Luca Ceresoli <luca.ceresoli@comelit.it>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Ben Warren <biggerbadderben@gmail.com>
Cc: Mike Frysinger <vapier@gentoo.org>