net/net.c: cosmetic: parentheses not required for return

This removes the following checkpatch issue:
 - ERROR: return is not a function, parentheses are not required

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