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



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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: Guangbin Huang <huangguangbin2@huawei.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Yongxin Li <liyongxin1@huawei.com>
Signed-off-by: Junxin Chen <chenjunxin1@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>