Fixes this error:
```
drivers\unix\ip_unix.cpp(155): error C2593: 'operator =' is ambiguous
.\core/ustring.h(177): note: could be 'void String::operator =(const CharType *)'
.\core/ustring.h(176): note: or       'void String::operator =(const char *)'
drivers\unix\ip_unix.cpp(155): note: while trying to match the argument list '(String, int)'
```