add () on SOPT_SIZE_CMSG_PKTINFO_IPV4() use, to match def.
Thanks to Hasso for code review.
diff --git a/lib/sockopt.h b/lib/sockopt.h
index cd79718..8d775cd 100644
--- a/lib/sockopt.h
+++ b/lib/sockopt.h
@@ -53,7 +53,7 @@
((af == AF_INET) ? SOPT_SIZE_CMSG_PKTINFO_IPV4() \
: SOPT_SIZE_CMSG_PKTINFO_IPV6()
-#define SOPT_SIZE_CMSG_IFINDEX_IPV4() SOPT_SIZE_CMSG_PKTINFO_IPV4
+#define SOPT_SIZE_CMSG_IFINDEX_IPV4() SOPT_SIZE_CMSG_PKTINFO_IPV4()
#elif defined (IP_RECVIF)
/* BSD/Solaris. Arguably these should say RECVIF rather than IFINDEX. */