Alter DHCP address selection after DECLINE in consec-addr mode.

Avoid offering the same address after a recieving a DECLINE message
to stop an infinite protocol loop. This has long been done in
default address allocation mode: this adds similar behaviour
when allocaing addresses consecutively.

src/dhcp.c

@@ -754,6 +754,19 @@ int address_allocate(struct dhcp_context *context,
 	      if (addr.s_addr == d->router.s_addr)
 		break;
 
+	    /* in consec-ip mode, skip addresses equal to
+	       the number of addresses rejected by clients. This
+	       should avoid the same client being offered the same
+	       address after it has rjected it. */
+	    if (option_bool(OPT_CONSEC_ADDR))
+	      {
+		if (c->addr_epoch)
+		  {
+		    c->addr_epoch--;
+		    d = context; /* d non-NULL skips the address. */
+		  }
+	      }
+	    
 	    /* Addresses which end in .255 and .0 are broken in Windows even when using 
 	       supernetting. ie dhcp-range=192.168.0.1,192.168.1.254,255,255,254.0
 	       then 192.168.0.255 is a valid IP address, but not for Windows as it's