[ipoib] Always set the "full membership" bit in the IPv4 broadcast GID

The SM always creates the IPoIB multicast groups with full membership
partition keys.

src/drivers/net/ipoib.c

 		 sizeof ( mac->gid.u.half[0] ) );
 
 	/* Update broadcast GID based on potentially-new partition key */
-	ipoib->broadcast.gid.u.words[2] = htons ( ibdev->pkey );
+	ipoib->broadcast.gid.u.words[2] =
+		htons ( ibdev->pkey | IB_PKEY_FULL );
 
 	/* Set net device link state to reflect Infiniband link state */
 	rc = ib_link_rc ( ibdev );

src/include/gpxe/infiniband.h

 /** Default Infiniband partition key */
 #define IB_PKEY_DEFAULT 0xffff
 
+/** Infiniband partition key full membership flag */
+#define IB_PKEY_FULL 0x8000
+
 /**
  * Maximum payload size
  *