bankd: Don't use 127.0.0.1 as default IP address for the server

If remsim-bankd connects via 127.0.0.1 or any other loopback-routed
IP address to the remsim-server, then the getpername() of remsim-server
for the bankd will also render 127.0.0.1, and subsequently that IP
address will be provided to remsim-client as address to connect to.

In almost all setups, remsim-client will be running on a remote node and
hence not able to reach remsim-bankd at 127.0.0.1.

Let's turn the server-IP into a mandatory command line argument of
remsim-bankd and not use a problematic default value.

Change-Id: I3deb05e31cdf35232cf9a118d5a5fcdb5d0ab601
diff --git a/doc/manuals/chapters/remsim-bankd.adoc b/doc/manuals/chapters/remsim-bankd.adoc
index 4df0844..e87de52 100644
--- a/doc/manuals/chapters/remsim-bankd.adoc
+++ b/doc/manuals/chapters/remsim-bankd.adoc
@@ -61,7 +61,7 @@
 
 ==== SYNOPSIS
 
-*osmo-remsim-bankd* [-h] [-V] [-d LOGOPT] [-i A.B.C.D] [-p <1-65535>] [-b <1-1023>] [-n <1-1023>] [-I A.B.C.D] [-P <1-65535> ]
+*osmo-remsim-bankd* [-h] [-V] [-d LOGOPT] -i A.B.C.D [-p <1-65535>] [-b <1-1023>] [-n <1-1023>] [-I A.B.C.D] [-P <1-65535> ]
 
 ==== OPTIONS
 
@@ -73,7 +73,9 @@
   Configure the logging verbosity, see <<remsim_logging>>.
 *-i, --server-host A.B.C.D*::
   Specify the remote IP address/hostname of the `osmo-remsim-server` to
-  which this bankd shall establish its RSPRO control connection
+  which this bankd shall establish its RSPRO control connection.  Do not specify a loopback
+  address or localhost, as this would in most cases result in a broken configuration where
+  a [usually remote] remsim-client attempts to reach the bankd via loopback, which doesn't work.
 *-p, --server-port <1-65535>*::
   Specify the remote TCP port number of the `osmo-remsim-server` to which
   this bankd shall establish its RSPRO control connection