net/bnxt: fix speed change from 200G to 25G on Thor

[ upstream commit 753b8ff26162ffaf118c03e47ab75cfd2229d4e8 ]

While forcing speed to 200G, driver sets the structure variable
"bp->link_info->link_signal_mode" value to BNXT_SIG_MODE_PAM4.
After that when the user forces the speed back to 25G, this
cached value is not set back to BNXT_SIG_MODE_NRZ which results
in issuing the HWRM_PORT_PHY_CFG command with wrong inputs.

Fixes: c23f9de ("net/bnxt: support 200G PAM4 link")

Signed-off-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Signed-off-by: Ajit Khaparde <ajit.khaparde@broadcom.com>
Reviewed-by: Somnath Kotur <somnath.kotur@broadcom.com>

drivers/net/bnxt/bnxt_hwrm.c

@@ -3005,6 +3005,7 @@ static uint16_t bnxt_parse_eth_link_speed(uint32_t conf_link_speed,
 	case RTE_ETH_LINK_SPEED_25G:
 		eth_link_speed =
 			HWRM_PORT_PHY_CFG_INPUT_AUTO_LINK_SPEED_25GB;
+		link_info->link_signal_mode = BNXT_SIG_MODE_NRZ;
 		break;
 	case RTE_ETH_LINK_SPEED_40G:
 		eth_link_speed =