Changed delta_generator to make use of --max_threads

Adding an option to configure max number of threads used during
ota_from_target_files

Bug: 277794445
Test: tested ota_from_target_files
Change-Id: I9bae92ee43c21926434ab04563a2b4f0678b73eb
diff --git a/scripts/brillo_update_payload b/scripts/brillo_update_payload
index 6652b38..083bfc2 100755
--- a/scripts/brillo_update_payload
+++ b/scripts/brillo_update_payload
@@ -222,6 +222,8 @@
     "Compression parameter passed to mkfs.erofs's -z option."
   DEFINE_string security_patch_level "" \
     "Optional: security patch level of this OTA"
+  DEFINE_string max_threads "" \
+    "Optional: specifies max_threads used to generate OTA"
 fi
 if [[ "${COMMAND}" == "hash" || "${COMMAND}" == "sign" ]]; then
   DEFINE_string unsigned_payload "" "Path to the input unsigned payload."
@@ -761,6 +763,11 @@
       --disable_vabc="${FLAGS_disable_vabc}" )
   fi
 
+  if [[ -n "${FLAGS_max_threads}" ]]; then
+    GENERATOR_ARGS+=(
+      --max_threads="${FLAGS_max_threads}" )
+  fi
+
   # minor version is set only for delta or partial payload.
   if [[ -n "${FORCE_MINOR_VERSION}" ]]; then
     GENERATOR_ARGS+=( --minor_version="${FORCE_MINOR_VERSION}" )