TOS bits != DSCP

We have VTY options that allow to set the DSCP value.  However, we
then call a function to set the TOS bits in the kernel.  This is
very wrong.  The DSCP is only the upper 6 bits of the 8-bit TOS
value, and hence we are mussing that translation.

As libosmocore now has a helper function osmo_sock_set_dscp(),
let's make use of it and don't care about the low-level details.

However, this means we need to finally remove the deprecated
alias for "rtp ip-tos <0-255>".

Closes: OS#5137
Change-Id: I9c18c90273be97aedd2ad212b82f650e35c32851
Depends: libosmocore.git Ia4ba389a5b7e3e9d5f17a742a900d6fd68c08e40
diff --git a/TODO-RELEASE b/TODO-RELEASE
index c5a3b36..add44f1 100644
--- a/TODO-RELEASE
+++ b/TODO-RELEASE
@@ -24,3 +24,4 @@
 # If any interfaces have been removed or changed since the last public release, a=0.
 #
 #library		what		description / commit summary line
+update dependency to libosmocore > 1.5.1 for our use of osmo_sock_set_dscp()