network: fix incorrect VIR_NETWORK_UPDATE_COMMAND_* values

network: fix incorrect VIR_NETWORK_UPDATE_COMMAND_* values

These enums originally were put into the flags for virNetworkUpdate,
and when they were moved into their own enum, the numbers weren't
appropriately changed, causing the commands to start with value 2
instead of 1. This causes problems for things like ENUM_IMPL, which
wants a string for every value in the requested range, including those
not used in the enum.