The current number of yet to be fully established connections.
This gauge is incremented when a connection is attempted, and
decremented when:
1. The connection becomes active. TCP connections become
active when the three-way connection establishment
handshake completes. UDP and ICMP, although connectionless
protocols, are modeled as connected when at least one
return packet is seen.
2. The connection attempt is timed out due to no response
from the destination.