This is to track the backporting of various upstream PRs leading up to the goal of the P2P network encapsulation:

• net: Split DNS resolving functionality out of net structures bitcoin/bitcoin#7868 (Done in [Net] Split DNS resolving functionality out of net structures #1360)
• Banlist updates bitcoin/bitcoin#7350 (Done in [Net] Banlist updates #1363)
• Call init's parameter interaction before we create the UI options model bitcoin/bitcoin#6780 (Done in [Init] Do parameter interaction before creating the UI model #1375)
• Combine common error strings for different options so translations can be shared and reused bitcoin/bitcoin#7257 (Done in [Init] Combine common error strings so translations can be shared #1376)
• Fix de-serialization bug where AddrMan is left corrupted bitcoin/bitcoin#7696 (Done in [Net] Fix de-serialization bug where AddrMan is corrupted after exception #1378)
• Add support for dnsseeds with option to filter by servicebits bitcoin/bitcoin#8083 (Done in [Net] Add support for dnsseeds with option to filter by servicebits #1452)
• Addrman offline attempts bitcoin/bitcoin#8065 (Done in [Net] Addrman offline attempts #1453)
• net: Add and document network messages in protocol.h bitcoin/bitcoin#7181 (Done in [Net] Add and document network messages in protocol.h #1542)
• chainparams: use SeedSpec6's rather than CAddress's for fixed seeds bitcoin/bitcoin#6059 (Done in [Net] Use SeedSpec6's rather than CAddress's for fixed seeds #1579)
• Enforce expected outbound services bitcoin/bitcoin#7749 (Done in [P2P] Enforce expected outbound services #1616)
• Do not set extra flags for unfiltered DNS seed results bitcoin/bitcoin#8208 (Done in [P2P] Do not set extra flags for unfiltered DNS seed results #1618)
• Fix masking of irrelevant bits in address groups. bitcoin/bitcoin#6556 (Done in [Net] Fix masking of irrelevant bits in address groups #1638)
• Rework addnode behaviour bitcoin/bitcoin#8113 (Done in [P2P][RPC] Rework addnode behaviour #1640)
• Net: Turn net structures into dumb storage classes bitcoin/bitcoin#8128 (Done in [Net] Turn net structures into dumb storage classes #1646)
• net: Feeler connections to increase online addrs in the tried table. bitcoin/bitcoin#8282 (Done in [Net] Pre-requirements for network encapsulation #1704)
• [Trivial] Do not shadow variables in networking code bitcoin/bitcoin#8466 (Done in [P2P] Begin Network Encapsulation #1812)
• Fix some locks bitcoin/bitcoin#8606 (Done in [P2P] Begin Network Encapsulation #1812)
• p2p: Begin encapsulation bitcoin/bitcoin#8085 (Done in [P2P] Begin Network Encapsulation #1812)
• net: drop boost::thread_group bitcoin/bitcoin#9289 (Done in [P2P] Begin Network Encapsulation #1812)
• net: No longer send local address in addrMe bitcoin/bitcoin#8740 (Done in [P2P] Begin Network Encapsulation #1812)
• Do not set an addr time penalty when a peer advertises itself. bitcoin/bitcoin#8661 (Done in [P2P] Begin Network Encapsulation #1812)