if_uba.c routines do not handle local net hlen of 0

[Schwab]

Description:
	If a local network interface has an hlen of 0, the routines
	in if_ubainit() allocate spurious pages and the if_rubaget()
	routine will exchange the wrong page when handling a packet
	greater than 1024 bytes long.
Repeat-By:
	The pcl-11 is such a device.  If you raise the mtu on the
	device from the default 1006 to anything greater than
	1024, your network will be unusable.
Fix:
	The following diff's fix the extraneous page allocations and
	the problems in if_rubaget().

			- Jeff Schwab
			  <jrs at purdue,  ...pur-ee!pucc-h:acg>

---- if_ubainit() ------
  	register caddr_t cp;
  	int i, ncl;
  
+ #ifdef	PUCC
+ 	ncl = clrnd(nmr + (hlen? CLSIZE: 0)) / CLSIZE;
+ #else	PUCC
  	ncl = clrnd(nmr + CLSIZE) / CLSIZE;
+ #endif	PUCC
  	if (ifu->ifu_r.ifrw_addr)
+ #ifdef	PUCC
+ 		cp = ifu->ifu_r.ifrw_addr - (hlen? (CLBYTES - hlen): 0);
+ #else	PUCC
  		cp = ifu->ifu_r.ifrw_addr - (CLBYTES - hlen);
+ #endif	PUCC
  	else {
  		cp = m_clalloc(2 * ncl, MPG_SPACE);
  		if (cp == 0)
  			return (0);
+ #ifdef	PUCC
+ 		ifu->ifu_r.ifrw_addr = cp + (hlen? (CLBYTES - hlen): 0);
+ #else	PUCC
  		ifu->ifu_r.ifrw_addr = cp + CLBYTES - hlen;
+ #endif	PUCC
  		ifu->ifu_w.ifrw_addr = ifu->ifu_r.ifrw_addr + ncl * CLBYTES;
------- if_rubaget() -------
  			ppte = &Mbmap[mtocl(p)*CLSIZE];
  			x = btop(cp - ifu->ifu_r.ifrw_addr);
  			ip = (int *)&ifu->ifu_r.ifrw_mr[x];
+ #ifdef	PUCC
+ 			if (ifu->ifu_hlen == 0) {
+ 				ip--;
+ 			}
+ #endif	PUCC
  			for (i = 0; i < CLSIZE; i++) {
  				struct pte t;
  				t = *ppte; *ppte++ = *cpte; *cpte = t;