vmxnet3: adjust ring sizes when interface is down

If ethtool is used to update ring sizes on a vmxnet3 interface that isn't
running, the change isn't stored, meaning the ring update is effectively is
ignored and lost without any indication to the user.

Other network drivers store the ring size update so that ring allocation uses
the new sizes next time the interface is brought up.  This patch modifies
vmxnet3 to behave this way as well

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
CC: "David S. Miller" <davem@davemloft.net>
CC: Shreyas Bhatewara <sbhatewara@vmware.com>
CC: "VMware, Inc." <pv-drivers@vmware.com>
Signed-off-by: David S. Miller <davem@davemloft.net>