vmxnet3: fix non static symbol warning

Fixes the following sparse warning:

drivers/net/vmxnet3/vmxnet3_drv.c:1645:1: warning:
 symbol 'vmxnet3_rq_destroy_all_rxdataring' was not declared. Should it be static?

Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Shrikrishna Khare <skhare@vmware.com>
Signed-off-by: David S. Miller <davem@davemloft.net>