nxstyle: Does not do sufficient name checking

The coding standard document (https://cwiki.apache.org/confluence/display/NUTTX/Coding+Standard) specifies the naming standards to be used in C source files. This includes case and naming ornmentation. For example, structure names should be all lower case and end with the suffix _s. Unions and enums are similar but should end in _u and _e, respectively. Global variable names should be lower case and begin with the prefix g_.

None of here are checked. I recently saw code with:

struct XYZ
{
int16_t d[3];
};

No error was reported even though the structure name is upper case and does not contain the prefix _s.