Resolve FIXMEs in src/net.cpp (pass config through CConnman)

Summary: The config is added to CConnman so that its member functions can access it.

Test Plan:
make check
../qa/pull-tester/rpc-tests.py

Reviewers: #bitcoin_abc, sickpig, awemany, dagurval, CCulianu, freetrader

Reviewed By: #bitcoin_abc, dagurval, CCulianu

Differential Revision: https://reviews.bitcoinabc.org/D311