Remove unused variable dfd.
 [jmk] --rw-rw-r-- M 284191 glenda sys 34865 Sep  7 10:38 sys/src/cmd/ip/ipconfig.c
	/n/sourcesdump/2005/0907/plan9/sys/src/cmd/ip/ipconfig.c:37,43 - 
	/n/sources/plan9/sys/src/cmd/ip/ipconfig.c:37,42
	  	char	*dev;
	  	char	mpoint[32];
	  	int	cfd;			// ifc control channel
	- 	int	dfd;			// ifc data channel (for ppp)
	  	char	*cputype;
	  	uchar	hwa[32];		// hardware address
	  	int	hwatype;
 [sys] --rwxrwxr-x M 284191 glenda sys 137742 Sep  7 23:07 386/bin/ip/ipconfig
	/sys/src/cmd/ip/ipconfig.c:dhcpquery
	/sys/src/cmd/ip/ipconfig.c:dhcprecv
	/sys/src/cmd/ip/ipconfig.c:dhcpsend
	/sys/src/cmd/ip/ipconfig.c:dhcptimer
	/sys/src/cmd/ip/ipconfig.c:dhcpwatch
	/sys/src/cmd/ip/ipconfig.c:doadd
	/sys/src/cmd/ip/ipconfig.c:doremove
	/sys/src/cmd/ip/ipconfig.c:getndb
	/sys/src/cmd/ip/ipconfig.c:ipconfig
	/sys/src/cmd/ip/ipconfig.c:ipunconfig
	/sys/src/cmd/ip/ipconfig.c:main
	/sys/src/cmd/ip/ipconfig.c:mkclientid
	/sys/src/cmd/ip/ipconfig.c:ndbconfig
	/sys/src/cmd/ip/ipconfig.c:openlisten
	/sys/src/cmd/ip/ipconfig.c:parsebootp
	/sys/src/cmd/ip/ipconfig.c:putndb