[sonic-linkmgrd] submodule update (#9343)

Submodule update for sonic-linkmgrd
Incorporates:

c11a576 (2021-11-22 09:38:46) [ci]: show code coverage in azure pipeline (#4)
4ceb01d (2021-11-18 20:24:20) Fix MUX toggling issue (#1)
d640527 (2021-11-12 22:31:44) [ci]: fix artifact download
b9f247d (2021-11-12 22:31:44) [ci]: use native arm64/armhf build
3059122 (2021-09-27 11:32:23) [linkgrd] Add Missing Apache License Header

signed-off-by: Jing Zhang zhangjing@microsoft.com