lxd/device/nic/ipvlan: Dont give sysctl read error when invalid value
lxd/device/nic/ipvlan: Dont give sysctl read error when invalid value

There is a check for this later with a better error message.

Signed-off-by: Thomas Parrott <6b778ce645fb0e3dde76d79eccad490955b1ae74@canonical.com>

hallyn/lxd,hallyn/lxd,stgraber/lxd,hallyn/lxd,lxc/lxd,stgraber/lxd,stgraber/lxd,lxc/lxd,stgraber/lxd,lxc/lxd,stgraber/lxd,hallyn/lxd,hallyn/lxd,atxwebs/lxd,lxc/lxd,hallyn/lxd,lxc/lxd,lxc/lxd,stgraber/lxd,atxwebs/lxd,lxc/lxd,stgraber/lxd,atxwebs/lxd,atxwebs/lxd