misc: Doxygen tweaks: fixed some typos and minor errors

Doxygen generates quite a lot of warnings on libosmocore. Some of them
are obvious typos - this patch aims to fix such low-hanging fruit.
diff --git a/include/osmocom/gsm/lapd_core.h b/include/osmocom/gsm/lapd_core.h
index 0f4e889..c2fdc62 100644
--- a/include/osmocom/gsm/lapd_core.h
+++ b/include/osmocom/gsm/lapd_core.h
@@ -11,9 +11,9 @@
  *  @{
  */
 
-/*! \file lapd.h */
-
-/* primitive related sutff */
+/*! \file lapd_core.h
+ * primitive related stuff
+ */
 
 /*! \brief LAPD related primitives (L2<->L3 SAP)*/
 enum osmo_dl_prim {
@@ -168,4 +168,6 @@
 int lapd_ph_data_ind(struct msgb *msg, struct lapd_msg_ctx *lctx);
 int lapd_recv_dlsap(struct osmo_dlsap_prim *dp, struct lapd_msg_ctx *lctx);
 
+/*! @} */
+
 #endif /* _OSMOCOM_LAPD_H */