Multiple bridges per host

Refactoring that allows enables Bitmask to handle providers that have more than one obfs4 bridge per host correctly. The refactoring also allows us to filter gateways for transport layer protocols (tcp, udp, kcp) in addition to transport types (openvpn, obfs4, obfs4_hop).

closes #9188 (closed)

part of QA during RC testing: #9186 (closed)