Add FAQ topic about bandwidth throttling (#2225)

filebeat/docs/faq.asciidoc

@@ -54,4 +54,5 @@ Filebeat uses a newline character to detect the end of an event. If lines are ad
 harvested, a newline character is required after the last line, or Filebeat will not read the last line of
 the file.
 
+include::../../libbeat/docs/faq-limit-bandwidth.asciidoc[]
 include::../../libbeat/docs/shared-faq.asciidoc[]

libbeat/docs/faq-limit-bandwidth.asciidoc

@@ -0,0 +1,20 @@
+[float]
+[[bandwidth-throttling]]
+=== Need to limit bandwidth used by {beatname_uc}?
+
+If you need to limit bandwidth usage, we recommend that you configure the network stack on your OS to perform
+bandwidth throttling.
+
+For example, the following Linux commands cap the connection between {beatname_uc} and Logstash by setting a
+limit of 50 kbps on TCP connections over port 5044:
+
+[source,shell]
+----------------------------------------------------------------------
+tc qdisc add dev $DEV root handle 1: htb
+tc class add dev $DEV parent 1:1 classid 1:10 htb rate 50kbps ceil 50kbps
+tc filter add dev $DEV parent 1:0 prio 1 protocol ip handle 10 fw flowid 1:10
+iptables -A OUTPUT -t mangle -p tcp --dport 5044 -j MARK --set-mark 10
+----------------------------------------------------------------------
+
+Using OS tools to perform bandwidth throttling gives you better control over policies. For example, you can use
+OS tools to cap bandwidth during the day, but not at night. Or you can leave the bandwidth uncapped, but assign a low priority to the traffic.

metricbeat/docs/faq.asciidoc

@@ -18,4 +18,5 @@ sudo mkdir -p /compat/linux/proc
 sudo mount -t linprocfs /dev/null /compat/linux/proc
 ----
 
+include::../../libbeat/docs/faq-limit-bandwidth.asciidoc[]
 include::../../libbeat/docs/shared-faq.asciidoc[]

packetbeat/docs/faq.asciidoc

@@ -72,4 +72,5 @@ To process long running transactions, you can specify a larger value for the <<t
 option. However, keep in mind that very large timeout values can increase memory usage if messages are lost or transaction
 response messages are not sent. 
 
+include::../../libbeat/docs/faq-limit-bandwidth.asciidoc[]
 include::../../libbeat/docs/shared-faq.asciidoc[]