Monitoring routine does not correctly set starting time in 1.3.6

When we backported the fix for GODRIVER-1695, we added a topology.Server.createConnection method, which creates the connection that's used for heartbeats. This caused a bug in the 1.3.6 release because we're no longer setting the start time in the WithHandshaker connection option as we were in 1.3.5 (https://github.com/mongodb/mongo-go-driver/commit/61c371255d98bb1a9556ad0f5b38d48635a24bbf#diff-cc0b094d8ce69672d7e2ff6da8ff60f5L479).

The 1.4.0 code does connection handshake RTT by storing fields on the connection type itself, so we should make a 1.3.x-only fix for this.