Support DSM 6 and 7

Small changes for DSM 6:

All fields (except enable_syno_token as explained below) must either be in the GET params or the POST params, you can't mix GET and POST params
enable_syno_token=yes must be in both the GET and POST params.
If enable_syno_token=yes is only in the POST fields, then DSM6 returns a synotoken of --------. If enable_syno_token=yes is only in the GET params, then it returns no synotoken at all. It must be in both to work.
Need to use /webapi/auth.cgi instead of /webapi/entry.cgi
Verified with DSM 6.2.3-25426 Update 2 and DSM 7.0-40850

deploy/synology_dsm.sh

@@ -90,7 +90,7 @@ synology_dsm_deploy() {
     _debug3 H1 "${_H1}"
   fi
 
-  response=$(_post "method=login&account=$encoded_username&passwd=$encoded_password&enable_device_token=yes&enable_syno_token=yes" "$_base_url/webapi/entry.cgi?api=SYNO.API.Auth&version=$api_version")
+  response=$(_post "method=login&account=$encoded_username&passwd=$encoded_password&api=SYNO.API.Auth&version=$api_version&enable_syno_token=yes" "$_base_url/webapi/auth.cgi?enable_syno_token=yes")
   token=$(echo "$response" | grep "synotoken" | sed -n 's/.*"synotoken" *: *"\([^"]*\).*/\1/p')
   _debug3 response "$response"
   _debug token "$token"