ctld: Return from the inner "main" loop on EINTR

This ensures that child processes are reaped in the outer loop in
main().

PR: 294035
Reviewed by: asomers
Fixes: 66b107e82b2f ("ctld: Use kevent(2) for socket events rather than select(2)")
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D56525