include config.h from lib/socket.c and use this to conditionaly

compile code to set sin_len on platforms that require this field
in the sockaddr structures.

Makefile.in

@@ -4,7 +4,7 @@ libdir = @libdir@
 bindir = @bindir@
 LIBS="-lpopt"
 CC=gcc
-CFLAGS=-g -O0 -fPIC -Wall -W -I./include "-D_U_=__attribute__((unused))"
+CFLAGS=-g -O0 -fPIC -Wall -W -I. -I./include "-D_U_=__attribute__((unused))"
 LIBISCSI_OBJ = lib/connect.o lib/crc32c.o lib/discovery.o lib/init.o lib/login.o lib/nop.o lib/pdu.o lib/scsi-command.o lib/scsi-lowlevel.o lib/socket.o lib/sync.o
 INSTALLCMD = /usr/bin/install -c