Limit the number of TCP connections that will be handled at one time.

Limit the number of TCP connections that will be handled at one time.
Remove some debugging calls.

* network.c (struct connection): New field start_time.
(tcp_data_counter, max_tcp_data_connections): New variables.
(kill_tcp_connection): New function.
(process_tcp_connection): Use it.  Log reason for rejecting connection if the
requested buffer size is too large.
(accept_tcp_connection): If there are too many TCP connections already, shut
down the oldest one.
(setup_network, listen_and_process, process_tcp_connection, service_conn):
Delete debugging code.
(process_packet): Use socklen_t where appropriate.

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@14903 dc483132-0cff-0310-8789-dd5450dbe970