For and exit so that inetd can have us be a "wait" service.

For and exit so that inetd can have us be a "wait" service.
The problem with the old way is that there is a race between tftpd (starting
up) and inetd (after forking and execing) to see who gets to read from port
69 (the udp port).  If inetd wins, it will spawn another instance of tftpd.
So, we read the packet from port 69, then fork and the parent returns.

SCCS-vsn: libexec/tftpd/tftpd.c 5.6