net: netcp: Fixes the use of spin_lock_bh in timer function

This patch fixes a bug in which the timer routine synchronized
against the ethtool-triggered statistics updates with spin_lock_bh().
A timer function is itself a bottom-half, so this should be
spin_lock().

Signed-off-by: WingMan Kwok <w-kwok2@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>