[orchagent] Change log level from ERR to WARN for pfc asym not supported

[zhixzhu]

What I did Change log level from ERR to WARN for pfc asym not supported

Why I did it To address issue reported in https://migsonic.atlassian.net/browse/MIGSMSFT-473

How I verified it Load new debian on testbed and check the log.

cisco@r2-lc0:~$ sudo cat /var/log/syslog | grep "queryPortAttrCapabilities"
Apr 25 22:52:26.787428 r2-lc0 WARNING swss1#orchagent: :- queryPortAttrCapabilities: Failed to get attribute(SAI_PORT_ATTR_PRIORITY_FLOW_CONTROL_TX) capabilities
Apr 25 22:52:26.787846 r2-lc0 WARNING swss1#orchagent: :- queryPortAttrCapabilities: Failed to get attribute(SAI_PORT_ATTR_PRIORITY_FLOW_CONTROL_RX) capabilities
cisco@r2-lc0:~$ 

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