[portconfig] Check supported speeds before setting port speed

[ghost]

• Checking whether requested speed is supported by the port by
  reading related field of PORT_TABLE:EthernetXX table in APPL_DB.
  If the field is absent or something went wrong while reading,
  then anyway set the speed to the port.

Signed-off-by: Maksym Belei [email protected]

- What I did
Checking of supported speeds by the port has added. If the speed is unsupported, porconfig script will throw an exception and reject setting the speed to the port.

- How I did it
By reading and comparing field "supp_speed" of table PORT_TABLE:EthernetXX of APPL_DB with requested value of speed.
If there was something wrong during reading field "supp_speed", the speed will be set without checking.

- How to verify it
Execute command config interface speed with passing speed argument with value of unsupported speed.

- Previous command output (if the output of a command-line utility has changed)
Currently, command "sudo config interface speed" allows any value of speed parameter.

- New command output (if the output of a command-line utility has changed)
if to request to set some unsupported speed, portconfig script will throw an exception:

admin@sonic:~$ sudo config interface speed Ethernet36 40001
Unsupported speed 40001 for port Ethernet36. Available values: 1000,10000,25000,40000,50000,56000,100000

- Delails
Related PRs:
sonic-net/sonic-swss#1622
#1391

[dprital]

@maksymbelei95 - are you going to promote this PR ?

[pshulik]

@dprital, Could please review or add additional reviewer