Binding Codec does not provide leaf default value for identityref

With following model

leaf transport-type

{ type sfc-sl:sl-transport-type-def; default "sfc-sl:vxlan-gpe"; description "Transport type from service-locator.yang."; }

default statement value is parsed to string instead of IdentitySchemaNode,
which is unsuitable for codecs to determine real value and codecs returns NULL.