ue_id - service id vs instance id - wildcard handling

[PLeVasseur]

Thanks @lukas-he for reminding me to fill this in!

Here's the diff:

Before:

MAY have the service ID part of its ue_id set to 0xFFFF in order to match any type,
MAY have the service instance ID part of its ue_id set to 0x0000 in order to match any instance,

After:

MAY have the service ID part of its ue_id set to 0xFFFF in order to match any service type.
MAY have the service instance ID part of its ue_id set to 0xFFFF in order to match any service instance. 0x0000 is the default instance ID used when there is only a single instance of a service.

Functionally we aligned the service instance ID part to match with how wildcard was done for the service ID by using 0xFFFF for wildcard and have 0x0000 be a default instead.

For more details on where the service ID and service instance ID are used, check this section:

In particular this bit:

A UUri’s ue_id property value determines the type and instance of the service being referred to:
The value’s least significant 16 bits contain the service ID, representing the service interface type.
The value’s most significant 16 bits contain the service instance ID.

[lukas-he]

In a previous commit, the change in the up-spec has been addressed here. In a chat with @PLeVasseur, we discussed about aligning the wildcard handling according to here with that of the up-rust implementation here.