Fix sysctl for salt-master optimization

Due to incorrect structure of the metadata,
the optimizations for salt-master multicast
RPC were not applied.

Add the missing key 'kernel' in the structure.

PROD-27850

Change-Id: I433d55212bd6331e982b41a62168b12628fc2f13
(cherry picked from commit 6cabe355dd067d2ac23bcd784eab781dd4733229)
diff --git a/salt/master/single.yml b/salt/master/single.yml
index 8d36565..a4f25d4 100644
--- a/salt/master/single.yml
+++ b/salt/master/single.yml
@@ -4,11 +4,12 @@
 parameters:
   linux:
     system:
-      sysctl:
-        net.core.rmem_max: 16777216
-        net.core.wmem_max: 16777216
-        net.ipv4.tcp_rmem: 4096 87380 16777216
-        net.ipv4.tcp_wmem: 4096 87380 16777216
+      kernel:
+        sysctl:
+          net.core.rmem_max: 16777216
+          net.core.wmem_max: 16777216
+          net.ipv4.tcp_rmem: 4096 87380 16777216
+          net.ipv4.tcp_wmem: 4096 87380 16777216
   salt:
     master:
       accept_policy: auto_accept