net: respect -onlynet= when making outbound connections

Do not make outbound connections to hosts which belong to a network
which is restricted by `-onlynet`.

This applies to hosts that are automatically chosen to connect to and to
anchors.

This does not apply to hosts given to `-connect`, `-addnode`,
`addnode` RPC, dns seeds, `-seednodes`.

Fixes https://github.com/bitcoin/bitcoin/issues/13378
Fixes https://github.com/bitcoin/bitcoin/issues/22647
Supersedes https://github.com/bitcoin/bitcoin/pull/22651

test/functional/feature_proxy.py

@@ -280,7 +280,7 @@ class ProxyTest(BitcoinTestFramework):
             n3 = networks_dict(self.nodes[3].getnetworkinfo())
             assert_equal(NETWORKS, n3.keys())
             for net in NETWORKS:
-                if net == NET_I2P:
+                if net == NET_I2P or net == NET_ONION:
                     expected_proxy = ''
                 else:
                     expected_proxy = f'[{self.conf3.addr[0]}]:{self.conf3.addr[1]}'