fix(transports): support for the 'network' parameter was missing for 'sips' transports

Reviewer guidelines

The following requirements must be met before merging:

flexisip	done	N.A.	Tests added
	done	N.A.	Related MR pipelines succeeded
	done	N.A.	SHA1 consistency of cherry-picked commits
linphone-sdk	done	N.A.	On a tag... (Except for master, which is allowed to use yet-to-be-released versions of the SDK)
	done	N.A.	...From the corresponding branch
docs	done	N.A.	CHANGELOG up to date
	done	N.A.	wiki (public documentation) up to date

Je n'ai pas ajouté d'entrée dans le changelog car c'est une fonctionnalité qui n'est pas encore en "stable".

Closes FLEXISIP-802