Oslo is a great example. Obviously it used to be vastly all white people, non-muslims. Today there's an ever growing Muslim community. Most don't try to become accustom to local traditions. They don't even try to mingle but rather stay among each other (Muslim immigrants).

The problem is that this exact argument has been used by virtually every single racist nativist group in history. Americans might be less swayed by them now just because of how much of our history involves these groups making huge stinks about the newest wave of immigrants only to be proven laughably wrong. First it was the Germans, then it was the Irish, the Chinese, the Italians, the Polish, the Jews. But in virtually all cases after a generation or two descendents of these groups differ in only superficial ways. Strong subcultures only developed in communities that experienced significant persisting amounts of alienation over generations. As such I present to you the alternate conjecture that alienation from mainstream Norwegian society is what's keeping these immigrants from assimilating quickly rather than just something defective within them.

It's also kind of silly to assume that citizens have an obligation to associate in any particular way. And equally silly is that this apparent obligation is placed on the shoulders of members of the minority to associate with the majority rather than the other way around.

Now, is it racist and/or wrong for a white resident that can trace ancestry back generations to say "I do not want these Muslim immigrants here?"

Yes, it is wrong and it is racist. It is racist because such a view treats Muslim immigrants as a monolithic group by wanting to collectively ban or evict a population because of the actions of some of its members. It's also important to note that such an attitude would also contribute to the greater alienation of the immigrant population and thus prevent the cultural assimilation that this person is frustrated is not taking place.