[config] add support for command "config interface pfc asymmetric EthernetXXX on/off"

[leoli-nps]

- What I did
Add support for command "config interface pfc asymmetric EthernetXXX on/off".

- How I did it
Modify subcommand pfc asymmetric according to the adjustment of the command interface group.

- How to verify it

1. First execute the command and observe the print;
2. Then use the command pfc show asymmetric to view the results.

- Previous command output (if the output of a command-line utility has changed)

admin@sonic:~$ sudo config interface pfc asymmetric Ethernet0 on
Usage: config interface pfc asymmetric [OPTIONS] STATUS

Error: Invalid value for "status": invalid choice: Ethernet0. (choose from on, off)
admin@sonic:~$
admin@sonic:~$ pfc show asymmetric Ethernet0


Interface    Asymmetric
-----------  ------------
Ethernet0    N/A


admin@sonic:~$

- New command output (if the output of a command-line utility has changed)

admin@sonic:~$ sudo config interface pfc asymmetric Ethernet0 on
admin@sonic:~$
admin@sonic:~$ pfc show asymmetric Ethernet0


Interface    Asymmetric
-----------  ------------
Ethernet0    on


admin@sonic:~$
admin@sonic:~$ sudo config interface pfc asymmetric Ethernet0 off
admin@sonic:~$
admin@sonic:~$ pfc show asymmetric Ethernet0


Interface    Asymmetric
-----------  ------------
Ethernet0    off


admin@sonic:~$

Signed-off-by: leo.li leo.li@nephosinc.com