fix(core): remove duplicate -nameserver/-searchdomain prefix in pct create

The NS and SD variables already contain the -nameserver= and
-searchdomain= prefixes (set in advanced_settings). PR #12521
incorrectly added a second prefix when building PCT_OPTIONS_STRING,
resulting in '-nameserver -nameserver=8.8.8.8' which pct rejects.

Also fixes the misleading comment ('Add storage' -> 'Add searchdomain').

Fixes #12572

misc/build.func

@@ -3617,16 +3617,16 @@ build_container() {
 $PCT_OPTIONS_STRING"
   fi
 
-  # Add storage if specified
+  # Add searchdomain if specified
   if [ -n "$SD" ]; then
     PCT_OPTIONS_STRING="$PCT_OPTIONS_STRING
-  -searchdomain $SD"
+  $SD"
   fi
 
   # Add nameserver if specified
   if [ -n "$NS" ]; then
     PCT_OPTIONS_STRING="$PCT_OPTIONS_STRING
-  -nameserver $NS"
+  $NS"
   fi
 
   # Network configuration