RRM: Move wpabuf_resize() call into wpas_rrm_report_elem()

RRM: Move wpabuf_resize() call into wpas_rrm_report_elem()

wpabuf_resize() can handle the initial allocation of a wpabuf and all
the other callers of wpas_rrm_report_elem() were already using a pointer
to a pointer and a wpabuf_resize() call. Simplify this by resizing the
wpabuf (if needed) within wpas_rrm_report_elem() instead of having to
calculate the needed size in all the callers. Thsi is also fixing one of
the allocation sizes to use the correct size instead of a size of a
struct that has nothing to do with the allocation (but is larger than
the needed five octets, so does not break anything).

Signed-off-by: Jouni Malinen <j@w1.fi>