fix(freeradius): replace MySQL SUBSTRING_INDEX with PostgreSQL split_part

files/sites-available/default

@@ -443,7 +443,7 @@ authorize {
 	# Engineers → dynamic pool
 	if (&control:Tmp-String-1 == "engineer") {
 		update control {
-			Pool-Name := "engineers-%{sql:SELECT SUBSTRING_INDEX('%{User-Name}','@',-1)}"
+			Pool-Name := "engineers-%{sql:SELECT split_part('%{User-Name}', '@', 2)}"
 		}
 	}
 	#  If you are using /etc/smbpasswd, and are also doing mschap authentication, the un-comment this line, and configure the 'smbpasswd' module.
@@ -650,7 +650,7 @@ accounting {
 
     ### rebuild Pool-Name 
     update control {
-        Pool-Name := "engineers-%{sql:SELECT SUBSTRING_INDEX('%{User-Name}','@',-1)}"
+        Pool-Name := "engineers-%{sql:SELECT split_part('%{User-Name}', '@', 2)}"
     }
 
     ### apply only for engineers