Simplify CConnman::SocketSendData routine.

Summary: As per title. The orginial logic is very convoluted. used this simplification to debug D284 .

Test Plan:

make check
../qa/pull-tester/rpc-tests.py -extended

Reviewers: freetrader, sickpig, kyuupichan, awemany, #bitcoin_abc

Reviewed By: freetrader, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D288