vslib: add support for read-only port capabilities

[ds952811]

This is part of HLD: sonic-net/SONiC#924, sonic-net/SONiC#925

What I did
Add port capability query for AutoNeg and Link-Training

Why I did it
Fix the VS test failure for the port AutoNeg and Link-Training capability queries

How I verified it
Ran the sonic-swss/tests/test_port_an.py to verify

[kcudnik]

please fix compilation issues:

SwitchStateBase.cpp:1238:19: error: 'SAI_PORT_ATTR_SUPPORTED_LINK_TRAINING_MODE' was not declared in this scope
         attr.id = SAI_PORT_ATTR_SUPPORTED_LINK_TRAINING_MODE;
                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
SwitchStateBase.cpp:1238:19: note: suggested alternative: 'SAI_PORT_ATTR_SUPPORTED_AUTO_NEG_MODE'
         attr.id = SAI_PORT_ATTR_SUPPORTED_LINK_TRAINING_MODE;
                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                   SAI_PORT_ATTR_SUPPORTED_AUTO_NEG_MODE
SwitchStateBase.cpp: In member function 'virtual sai_status_t saivs::SwitchStateBase::refresh_read_only(const sai_attr_metadata_t*, sai_object_id_t)':
SwitchStateBase.cpp:2320:18: error: 'SAI_PORT_ATTR_SUPPORTED_LINK_TRAINING_MODE' was not declared in this scope
             case SAI_PORT_ATTR_SUPPORTED_LINK_TRAINING_MODE:
                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
SwitchStateBase.cpp:2320:18: note: suggested alternative: 'SAI_PORT_ATTR_SUPPORTED_AUTO_NEG_MODE'
             case SAI_PORT_ATTR_SUPPORTED_LINK_TRAINING_MODE:
                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                  SAI_PORT_ATTR_SUPPORTED_AUTO_NEG_MODE

[ds952811]

please fix compilation issues:

SwitchStateBase.cpp:1238:19: error: 'SAI_PORT_ATTR_SUPPORTED_LINK_TRAINING_MODE' was not declared in this scope
         attr.id = SAI_PORT_ATTR_SUPPORTED_LINK_TRAINING_MODE;
                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
SwitchStateBase.cpp:1238:19: note: suggested alternative: 'SAI_PORT_ATTR_SUPPORTED_AUTO_NEG_MODE'
         attr.id = SAI_PORT_ATTR_SUPPORTED_LINK_TRAINING_MODE;
                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                   SAI_PORT_ATTR_SUPPORTED_AUTO_NEG_MODE
SwitchStateBase.cpp: In member function 'virtual sai_status_t saivs::SwitchStateBase::refresh_read_only(const sai_attr_metadata_t*, sai_object_id_t)':
SwitchStateBase.cpp:2320:18: error: 'SAI_PORT_ATTR_SUPPORTED_LINK_TRAINING_MODE' was not declared in this scope
             case SAI_PORT_ATTR_SUPPORTED_LINK_TRAINING_MODE:
                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
SwitchStateBase.cpp:2320:18: note: suggested alternative: 'SAI_PORT_ATTR_SUPPORTED_AUTO_NEG_MODE'
             case SAI_PORT_ATTR_SUPPORTED_LINK_TRAINING_MODE:
                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                  SAI_PORT_ATTR_SUPPORTED_AUTO_NEG_MODE

It depends on the following PR in the SAI master branch, can I update the SAI submodule to use the latest commit of master branch?
opencomputeproject/SAI#1434

[kcudnik]

yes, you can raise PR to update submodule