Use proper struct sockpeercred for SO_PEERCRED for OpenBSD

getsockopt(2) documents this;  ucred is wrong ("cr_" member prefix, no pid).

(cherry picked from commit 10ccdb7a41)

src/nix/unix/daemon.cc

@@ -202,7 +202,11 @@ static PeerInfo getPeerInfo(int remote)
 
 #if defined(SO_PEERCRED)
 
-    ucred cred;
+# if defined(__OpenBSD__)
+   struct sockpeercred cred;
+# else
+   ucred cred;
+# endif
     socklen_t credLen = sizeof(cred);
     if (getsockopt(remote, SOL_SOCKET, SO_PEERCRED, &cred, &credLen) == -1)
         throw SysError("getting peer credentials");