This command serves no real purpose, offers no checking that the address
 entered is even a MN (which it shouldn't), and is essentially just a
 stripped down version of the addnode command.

The checking of the port in masternode.conf files was overly complex.
This simplifies it whilst maintaining that the port much match the
default P2P port for the current network and removes the reliance on
"magic numbers".

This also adds some sanity checking to masternode startup arguments:
* -listen can't be 0 when -masternode is 1
* when -masternode is set, require that the client uses the default port
* validate the port supplied (if any) for -masternodeaddr

Lastly, `CMasternodeBroadcast::CheckDefaultPort` now takes a `CService`
as it's first argument instead of a string.

Net functionality is no longer needed for CAddress/CAddrman/etc. now that
CNetAddr/CService/CSubNet are dumb storage classes.

Also fix up a few small issues:
- Lookup with "badip:port" now sets the port to 0
- Don't allow assert to have side-effects

apply clang-format