Rashi writes in Chulin Daf 106
"Basar Chazir Chamur mi'Neveilah d'Is Beih Trei Isurei"
What 2 issurim are there? There is such a thing as issur nevillah by chazir? What about "ain issur chal al issur"
Yehoshua, Yerushalayim, Eretz Yisrael
The Keser ha'Melech on the Rambam (Machalos Assuros ch. 4) says that it indeed is Neveilah and that Neveilah is Chal on the Issur of Temeiah. However, the Teshuvos Divrei Chachamim (Orach Chaim 103) says that this is referring to the prohibition of "Osah Tocheilu" which is a Lav ha'Ba mi'Chlal Asei along with the regular prohibition of Lo Socheilu.
All the best,
Yaakov Montrose