docs: ethtool: Add two link extended substates of bad signal integrity

mainline inclusion
from mainline-master
commit 958ab281
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I46N7D
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=958ab281eb3e0543a995457fd2d9cb4504cde4b8

----------------------------------------------------------------------

Add documentation for two bad signal integrity substates:
ETHTOOL_LINK_EXT_SUBSTATE_BSI_SERDES_REFERENCE_CLOCK_LOST
ETHTOOL_LINK_EXT_SUBSTATE_BSI_SERDES_ALOS.
Signed-off-by: NGuangbin Huang <huangguangbin2@huawei.com>
Signed-off-by: NJakub Kicinski <kuba@kernel.org>
Reviewed-by: NYongxin Li <liyongxin1@huawei.com>
Signed-off-by: NJunxin Chen <chenjunxin1@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

Documentation/networking/ethtool-netlink.rst

@@ -584,6 +584,14 @@ Link extended substates:
                                                                        that is not formally
                                                                        supported, which led to
                                                                        signal integrity issues
+
+  ``ETHTOOL_LINK_EXT_SUBSTATE_BSI_SERDES_REFERENCE_CLOCK_LOST``        The external clock signal for
+                                                                       SerDes is too weak or
+                                                                       unavailable.
+
+  ``ETHTOOL_LINK_EXT_SUBSTATE_BSI_SERDES_ALOS``                        The received signal for
+                                                                       SerDes is too weak because
+                                                                       analog loss of signal.
   =================================================================    =============================
 
   Cable issue substates: