[swss]: Update swss.sh script to clean up specific db when start

This script shall not flush all the entries in the state database
when it starts up, since there are entries maintained and written
by other processes outside this docker.

The issue we noticed was that the portchannel states are cleaned
up after teamsyncd writes the entries into the database, which
causes the IPs failed to be configured because intfmgrd considers
the portchannels are not ready yet.

Signed-off-by: Shu0T1an ChenG <shuche@microsoft.com>

files/scripts/swss.sh

@@ -62,6 +62,21 @@ function wait_for_database_service()
     done
 }
 
+# This function cleans up the tables with specific prefixes from the database
+# $1 the index of the database
+# $2 the string of a list of table prefixes
+function clean_up_tables()
+{
+    redis-cli -n $1 EVAL "
+    local tables = {$2}
+    for i = 1, table.getn(tables) do
+        local matches = redis.call('KEYS', tables[i])
+        for j,name in ipairs(matches) do
+            redis.call('DEL', name)
+        end
+    end" 0
+}
+
 start() {
     debug "Starting ${SERVICE} service..."
 
@@ -78,7 +93,7 @@ start() {
         /usr/bin/docker exec database redis-cli -n 0 FLUSHDB
         /usr/bin/docker exec database redis-cli -n 2 FLUSHDB
         /usr/bin/docker exec database redis-cli -n 5 FLUSHDB
-        /usr/bin/docker exec database redis-cli -n 6 FLUSHDB
+        clean_up_tables 6 "'PORT_TABLE*', 'MGMT_PORT_TABLE*', 'VLAN_TABLE*', 'VLAN_MEMBER_TABLE*', 'INTERFACE_TABLE*', 'MIRROR_SESSION*', 'WARM_RESTART_TABLE*'"
     fi
 
     # start service docker