Fix condition for concurrent link on linux_chromium_rel_ng builder

This is follow up of
https://chromium-review.googlesource.com/938883

This is for increase the number concurrent link on buildbot, does the same thing with below CL.
https://chromium-review.googlesource.com/891043

Bug: 794423
Change-Id: I2272cf8be22235b26f12568ccb6d5f55059538a5
Reviewed-on: https://chromium-review.googlesource.com/938688
Commit-Queue: Takuto Ikuta <tikuta@google.com>
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#539681}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: b6e0659b3aaeecd54ffd9401c05d081e00d50735

toolchain/concurrent_links.gni

@@ -43,7 +43,8 @@ if (concurrent_links == -1) {
     # make heavier use of ProGuard, and so should not be raised. Sanitizers also
     # increase the memory overhead.
     _args = [ "--mem_per_link_gb=4" ]
-  } else if (is_linux && !is_chromeos && symbol_level == 1) {
+  } else if (is_linux && !is_chromeos && symbol_level == 0) {
+    # Memory consumption on link without debug symbols is low on linux.
     _args = [ "--mem_per_link_gb=3" ]
   } else {
     _args = []