tg3: disable TSO and scatter-gather on 5714/5715/5780 on sparc64

The BCM5715 (5780_CLASS) hang on Sun PCI-X host bridges found in
sparc64 Ultra 25/45.

Observed on a BCM95715 rev 9003, i.e. ASIC_REV_5714 (PCIX:133MHz:64-bit):

  tg3 0000:07:04.0 eth0: NETDEV WATCHDOG: transmit queue 0 timed out
  tg3 0000:07:04.0 eth0: transmit timed out, resetting
  tg3 0000:07:04.0: tg3_stop_block timed out, ofs=2c00 enable_bit=2

Signed-off-by: René Rebe <rene@exactco.de>

--- linux-7.1/drivers/net/ethernet/broadcom/tg3.c.orig	2026-07-16 12:40:03.660589321 +0200
+++ linux-7.1/drivers/net/ethernet/broadcom/tg3.c	2026-07-16 12:40:03.660710386 +0200
@@ -16428,6 +16428,10 @@
 			tp->fw_needed = FIRMWARE_TG3TSO;
 	}
 
+	/* Sun Ultra 25/45 NetXtreme BCM5715 */
+	if (IS_ENABLED(CONFIG_SPARC64) && tg3_flag(tp, 5780_CLASS))
+		tg3_flag_clear(tp, HW_TSO_1);
+
 	/* Selectively allow TSO based on operating conditions */
 	if (tg3_flag(tp, HW_TSO_1) ||
 	    tg3_flag(tp, HW_TSO_2) ||