util/sockopt: fix forward-declaration of Log
We need a proper typedef-forward-declaration, rather than just the
struct. Fix it.
#include <c-macro.h>
#include <stdlib.h>
-struct Log;
+typedef struct Log Log;
int sockopt_get_peersec(int fd, char **labelp, size_t *lenp);
int sockopt_get_peergroups(int fd, Log *log, uid_t uid, gid_t gid, gid_t **gidsp, size_t *n_gidsp);
