manual: 'Running': tweak, mention 'tunmap' and 'tunend'

Change-Id: I9760ca214933d0b05080a3e70807b0cd06380a27
---
M doc/manuals/chapters/running.adoc
1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/doc/manuals/chapters/running.adoc b/doc/manuals/chapters/running.adoc
index 683c444..009ec16 100644
--- a/doc/manuals/chapters/running.adoc
+++ b/doc/manuals/chapters/running.adoc
@@ -85,11 +85,11 @@
 
 OsmoUPF uses two distinct Linux kernel features:
 
-* The GTP module is used for GTP encapsulation/decapsulation from/to
+* The GTP module is used for `tunend`: GTP encapsulation/decapsulation from/to
   "the internet".
 
-* The netfilter module is used for GTP tunnel proxying, also known as
-  tunnel forwarding or tunnel mapping.
+* The netfilter framework and nftables is used for `tunmap`: GTP tunnel proxying, 
+  also known as tunnel forwarding or tunnel mapping.
 
 .Linux kernel feature usage
 [graphviz]
@@ -97,8 +97,12 @@
 include::upf_gtp_roles.dot[]
 ----
 
-GTP kernel module configuration can be omitted for sites that serve only as GTP
-forwarding proxy, without encapsulation/decapsulation of GTP payloads.
+GTP kernel module configuration in the `tunend` section can be omitted for sites
+that serve only as GTP forwarding proxy, without encapsulation/decapsulation of
+GTP payloads.
+
+Likewise, netfilter configuration in the `tunmap` section can be omitted for
+sites only serving as GTP tunnel endpoint.
 
 [[gtp_module]]
 === Configure Linux Kernel GTP Module for `tunend`

