device/utils: Adds NetworkSRIOVGetFreeVFInterface function
device/utils: Adds NetworkSRIOVGetFreeVFInterface function

Used by nic sriov and infiniband sriov to find free virtual function interface on the same device and port as parent.

Signed-off-by: Thomas Parrott <6b778ce645fb0e3dde76d79eccad490955b1ae74@canonical.com>

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