mpm: document Search callback return value

src/util-mpm.h

@@ -159,6 +159,7 @@ typedef struct MpmTableElmt_ {
     int  (*AddPattern)(struct MpmCtx_ *, uint8_t *, uint16_t, uint16_t, uint16_t, uint32_t, SigIntId, uint8_t);
     int  (*AddPatternNocase)(struct MpmCtx_ *, uint8_t *, uint16_t, uint16_t, uint16_t, uint32_t, SigIntId, uint8_t);
     int  (*Prepare)(struct MpmCtx_ *);
+    /** \retval cnt number of patterns that matches: once per pattern max. */
     uint32_t (*Search)(const struct MpmCtx_ *, struct MpmThreadCtx_ *, PrefilterRuleStore *, const uint8_t *, uint32_t);
     void (*PrintCtx)(struct MpmCtx_ *);
     void (*PrintThreadCtx)(struct MpmThreadCtx_ *);