Everywhere: Replace a bundle of dbg with dbgln.

These changes are arbitrarily divided into multiple commits to make it
easier to find potentially introduced bugs with git bisect.Everything:

The modifications in this commit were automatically made using the
following command:

    find . -name '*.cpp' -exec sed -i -E 's/dbg\(\) << ("[^"{]*");/dbgln\(\1\);/' {} \;

Kernel/Net/Socket.cpp

@@ -188,7 +188,7 @@ KResult Socket::getsockopt(FileDescription&, int level, int option, Userspace<vo
     case SO_ERROR: {
         if (size < sizeof(int))
             return KResult(-EINVAL);
-        dbg() << "getsockopt(SO_ERROR): FIXME!";
+        dbgln("getsockopt(SO_ERROR): FIXME!");
         int errno = 0;
         if (!copy_to_user(static_ptr_cast<int*>(value), &errno))
             return KResult(-EFAULT);