New HAVE_STRUCT_SOCKADDR_SA_LEN macro

Only present if struct sockaddr.sa_len exists, to be checked with
preprocessor's #ifdef.

Refs #3154

configure.ac

@@ -502,6 +502,11 @@ AM_CONDITIONAL([WITH_PERSISTENT_STORAGE],
 
 AM_MISSING_HAS_RUN
 
+AC_CHECK_MEMBER([struct sockaddr.sa_len],
+	[AC_DEFINE([HAVE_STRUCT_SOCKADDR_SA_LEN], [1],
+		[Define if sa_len is present in struct sockaddr])],
+	[], [#include <sys/socket.h>])
+
 AC_CHECK_DECL([SO_ACCEPTFILTER],
     AC_DEFINE(HAVE_ACCEPT_FILTERS,1,[Define to 1 if you have accept filters]),
     ,