Increase the TCP timeout allowance from 1 second to 3

When starting a new TCP query, the initial SRTT estimate
includes time for the kernel to resend SYN if necessary. At
one second, the margin was not always sufficient; this commit
increases it to three.
67 jobs for !5264 with 2821-tcp-timeout-allowance-too-short in 21 minutes and 4 seconds (queued for 5 minutes and 54 seconds)
latest merge request