new: usr: Implement tcp-primaries-timeout
requested to merge 3649-configurable-xfr-tcp-timeouts into 5009-dispatch-separate-connect-and-read-timeouts
The new 'tcp-primaries-timeout' configuration option works the same way as the older 'tcp-initial-timeout' option, but applies only to the TCP connections made to the primary servers, so that the timeout value can be set separately for them. The default is 15 seconds.
Closes #3649
Edited by Arаm Sаrgsyаn