qcacmn: Fix dp_stats.c documentation

The kernel-doc script identified a large number of documentation
issues in dp/wifi3.0/dp_stats.c, so fix those issues. In addition,
there are a number of instances where public functions have their
implementation documented instead of having their interface
documented, so remove that documentation. The documentation at the
interface will be added separately if it is not already present.

Change-Id: Ic6463cb4acf49758ac78c4ac464b7e55133ecca4
CRs-Fixed: 3373155