[BUG] Importing networks fail because of json encoded strings in ndfc_networks resource

[pritispa]

Steps to reproduce:

1. Import networks from NDFC with config generate option (import block based import)
2. During apply operation it fails because of mismatch of json encoded string instance_values

╷
│ Error: Provider produced inconsistent result after apply
│ 
│ When applying changes to ndfc_networks.Staging_Fabric_Physical2_imported_networks, provider
│ "provider[\"registry.terraform.io/ciscodevnet/ndfc\"]" produced an unexpected new value:
│ .networks["nw_frog"].attachments["FDO28390AP6"].instance_values: was
│ cty.StringVal("{\"isActive\":\"false\",\"isVPC\":\"true\"}"), but now
│ cty.StringVal("{\"isVPC\":\"true\",\"isActive\":\"false\"}").

[akabhask]

Fix : #202