net: Use RCU_POINTER_INITIALIZER() to init static variable

This pointer is RCU protected, so proper primitives should be used.

Signed-off-by: Zhang Yu <zhangyu31@baidu.com>
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>