The netfilter module is now loaded on-demand, and no longer during daemon
startup, making these fields obsolete. These fields are now always `false`
and will be removed in the next relase.
This patch deprecates:
- the `BridgeNfIptables` field in `api/types/system.Info`
- the `BridgeNfIp6tables` field in `api/types/system.Info`
- the `BridgeNFCallIPTablesDisabled` field in `pkg/sysinfo.SysInfo`
- the `BridgeNFCallIP6TablesDisabled` field in `pkg/sysinfo.SysInfo`
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>