[ATMOSPHERE-437] Fix ethtool tuning for NICs without rx-{mini,jumbo} (#1847)

This is an automated cherry-pick of #1841
/assign mnaser
diff --git a/roles/ethtool/files/ethtool b/roles/ethtool/files/ethtool
index d5f7721..2daab18 100644
--- a/roles/ethtool/files/ethtool
+++ b/roles/ethtool/files/ethtool
@@ -19,5 +19,13 @@
 
   logger -sp info "atmosphere: ${i} max rx:${MAX_RX}, rxmini:${MAX_RX_MINI}, rxjumbo:${MAX_RX_JUMBO}, tx:${MAX_TX}"
 
-  ethtool -G ${i} rx ${MAX_RX} rx-mini ${MAX_RX_MINI} rx-jumbo ${MAX_RX_JUMBO} tx ${MAX_TX} || :
+  ethtool -G ${i} rx ${MAX_RX} tx ${MAX_TX} || :
+
+  if [ "$MAX_RX_MINI" != "n/a" ]; then
+    ethtool -G ${i} rx-mini ${MAX_RX_MINI} || :
+  fi
+
+  if [ "$MAX_RX_JUMBO" != "n/a" ]; then
+    ethtool -G ${i} rx-jumbo ${MAX_RX_JUMBO} || :
+  fi
 done