Use cash magic by default when etablishing connection to new peers.

Summary: Node still accept incomming connection from nodes that do not use the new cash magic. The deployed base of ABC and classic nodes taht do support the new cash magic is large enough.

Test Plan: Run a node using the new cash magic for a while. Assert it has peers that use the cash magic and others that do not using the getpeerinfo RPC.

Reviewers: freetrader, CCulianu, dagurval, #bitcoin_abc, schancel

Reviewed By: #bitcoin_abc, schancel

Subscribers: schancel

Differential Revision: https://reviews.bitcoinabc.org/D547