colliding interface names

[Ron Stanonik]

Description:
	Ioctl's can affect the wrong interface if you have interfaces
	with similar names; eg, sl and slip.  The problem is that
	ifunit(name), in sys/net/if.c, bcmp's its argument
	to each interface name, but doesn't compare lengths.  So,
	sl, being a prefix of slip, matches.  (I feel as though I've
	seen a fix for this, but couldn't find it.)  By the way, 4.3BSD
	seems to have the same bug.
Repeat-By:
	We have two serial interfaces, "sl" from rick at seismo.arpa,
	and "slip" from ks at purdue-ecn.arpa.  The "slip" interface
	was if_attach'ed first.  Ifconfig'ing "sl" clobbered the
	"slip" interface.
Fix:
--- if.c	Mon Dec 16 12:04:59 1985
***************
*** 184,190
  {
  	register char *cp;
  	register struct ifnet *ifp;
! 	int unit;
  
  	for (cp = name; cp < name + IFNAMSIZ && *cp; cp++)
  		if (*cp >= '0' && *cp <= '9')

--- 184,190 -----
  {
  	register char *cp;
  	register struct ifnet *ifp;
! 	int unit, len;
  
  	for (cp = name; cp < name + IFNAMSIZ && *cp; cp++)
  		if (*cp >= '0' && *cp <= '9')
***************
*** 192,197
  	if (*cp == '\0' || cp == name + IFNAMSIZ)
  		return ((struct ifnet *)0);
  	unit = *cp - '0', *cp = 0;
  	for (ifp = ifnet; ifp; ifp = ifp->if_next) {
  		if (bcmp(ifp->if_name, name, (unsigned)(cp - name)))
  			continue;

--- 192,198 -----
  	if (*cp == '\0' || cp == name + IFNAMSIZ)
  		return ((struct ifnet *)0);
  	unit = *cp - '0', *cp = 0;
+ 	len = (int)(cp - name);
  	for (ifp = ifnet; ifp; ifp = ifp->if_next) {
  		if (strlen(ifp->if_name) != len || bcmp(ifp->if_name, name, len))
  			continue;
***************
*** 193,199
  		return ((struct ifnet *)0);
  	unit = *cp - '0', *cp = 0;
  	for (ifp = ifnet; ifp; ifp = ifp->if_next) {
! 		if (bcmp(ifp->if_name, name, (unsigned)(cp - name)))
  			continue;
  		if (unit == ifp->if_unit)
  			break;

--- 194,200 -----
  	unit = *cp - '0', *cp = 0;
  	len = (int)(cp - name);
  	for (ifp = ifnet; ifp; ifp = ifp->if_next) {
! 		if (strlen(ifp->if_name) != len || bcmp(ifp->if_name, name, len))
  			continue;
  		if (unit == ifp->if_unit)
  			break;