echo_srv: Do not close bogus file descriptors

echo_srv: Do not close bogus file descriptors

==1564== Warning: invalid file descriptor 1048564 in syscall close()
==1564==    at 0x4D18534: close (in /lib64/libc-2.27.so)
==1564==    by 0x4046A74: libc_close (socket_wrapper.c:760)
==1564==    by 0x405105C: swrap_close (socket_wrapper.c:5933)
==1564==    by 0x40511F5: close (socket_wrapper.c:5979)
==1564==    by 0x401679: become_daemon (echo_srv.c:202)
==1564==    by 0x402D44: main (echo_srv.c:896)
==1563==

Signed-off-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>