Explicitly enable busmastering on PCI-PCI bridges. Transactions initiated

on the secondary side of a bridge will not be propagated to the primary
bus unless this is enabled.  Busmastering is not enabled by default (we
have relied on firmware to set this bit to date).  The OS needs to set it
for any bridges not configured by system firmware.

Tested by:	Steve Polyack  korvus comcast net
MFC after:	2 weeks

sys/dev/pci/pci_pci.c

@@ -683,6 +683,13 @@ pcib_attach_common(device_t dev)
      *     would be more widely routed than absolutely necessary.  We could
      *     then do a walk of the tree later and fix it.
      */
+
+    /*
+     * Always enable busmastering on bridges so that transactions
+     * initiated on the secondary bus are passed through to the
+     * primary bus.
+     */
+    pci_enable_busmaster(dev);
 }
 
 int