* gnu/services/ssh.scm (openssh-shepherd-service): Use
'make-inetd-constructor' when it is defined.
(<openssh-configuration>)[max-connections]: New field.
* gnu/tests/ssh.scm (run-ssh-test)["sshd PID"]: Adjust to cope with
PID-FILE being #f.
* gnu/tests/ssh.scm (%test-openssh): Pass #f as the 'pid-file'
argument.
* doc/guix.texi (Networking Services): Document 'max-connections'.