postfix: fix multilib conflict of sample-main.cf

It fails to install postfix and lib32-postfix at same time:

| Error: Transaction test error:
|   file /etc/postfix/sample-main.cf conflicts between attempted installs of
    lib32-postfix-cfg-3.7.3-r0.i586 and postfix-cfg-3.7.3-r0.core2_64

Rename sample-main.cf with ${MLPREFIX}.

Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>

meta-networking/recipes-daemons/postfix/postfix.inc

@@ -115,7 +115,7 @@ do_install () {
         'data_directory=${localstatedir}/lib/postfix' \
         -non-interactive
     rm -rf ${D}${localstatedir}/spool/postfix
-    mv ${D}${sysconfdir}/postfix/main.cf ${D}${sysconfdir}/postfix/sample-main.cf
+    mv ${D}${sysconfdir}/postfix/main.cf ${D}${sysconfdir}/postfix/${MLPREFIX}sample-main.cf
     install -m 755 ${S}/bin/smtp-sink ${D}/${sbindir}/
     install -d ${D}${sysconfdir}/init.d
     install -m 644 ${WORKDIR}/main.cf ${D}${sysconfdir}/postfix/main.cf