Use setresuid/gid() directly to change user and group.  Otherwise
Suricata uses libcap-ng on Linux and runs as root elsewhere.

Index: src/util-privs.h
--- src/util-privs.h.orig
+++ src/util-privs.h
@@ -92,6 +92,7 @@ void SCDropMainThreadCaps(uint32_t , uint32_t );
 
 void SCGetUserID(const char *, const char *, uint32_t *, uint32_t *);
 void SCGetGroupID(const char *, uint32_t *);
+int SCSetUserID(const uint32_t uid, const uint32_t gid);
 
 #ifdef __OpenBSD__
 int SCPledge(void);
