lxd/network/driver/ovn: Use client.LogicalSwitchDHCPOptionsGet in InstanceDevicePortSetup
lxd/network/driver/ovn: Use client.LogicalSwitchDHCPOptionsGet in InstanceDevicePortSetup

 - Adds support for detecting multiple conflicting DHCP options sets.
 - Reduces calls to ovn-nbctl.

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

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