Adjust default tcp-clients value upward

The default for tcp-clients is set at 150. As more users are now supporting encrypted DNS, which sessions use TCP, it is likely that the % of overall DNS sessions using TCP will increase, and the current default quota will be too low for many users. Although it is impossible to determine the ideal setting for all users, it seems likely that users who need to limit TCP sessions can support at least an order of magnitude more sessions, like maybe 2,000.

If we are very worried about impacting small-system users of BIND, perhaps we could just change the setting for BIND -S, which is not available to hobbyists?