initialise salen in binresvport_sa

avoids failures with UsePrivilegedPort=yes

patch from Juan Gallego
diff --git a/openbsd-compat/bindresvport.c b/openbsd-compat/bindresvport.c
index c89f214..eeb269d 100644
--- a/openbsd-compat/bindresvport.c
+++ b/openbsd-compat/bindresvport.c
@@ -64,6 +64,7 @@
 	if (sa == NULL) {
 		memset(&myaddr, 0, sizeof(myaddr));
 		sa = (struct sockaddr *)&myaddr;
+		salen = sizeof(myaddr);
 
 		if (getsockname(sd, sa, &salen) == -1)
 			return -1;	/* errno is correctly set */