Changes

release-tarball: support git submodules

osmo-trx 1.5.0 is now using a git submodule for osmocom-bb, so add
support for it.

Change-Id: I35e9ef6d976ae8cf2bfb4f3c410e6b2cb3ca7841

release-tarball: fix osmo-trx 1.5.0

Run configure with the --with-mstrx argument, so LIBTRXCON_DIR is not
pointing at an empty directory.

Fix for:
  make[2]: Entering directory '/build/_temp/repos/osmo-trx/osmocom-bb'
  make[2]: *** No rule to make target 'distdir'.  Stop.

Change-Id: I2f067409f98119d4e35cf86cc2c816fc3c19e3f5

release-tarball: remove PARALLEL_MAKE variable

Probably copy pasted from another script, doesn't make much sense here
since only the release tarballs are built. Nothing gets compiled here,
the variable was not used.

Change-Id: Ie74ee6976759f9634503b21e964e93efcc925679

release-tarball: add var to use list from jenkins

Add a parameter that can be used to reproduce the failure locally with
the last list from jenkins, without having SSH set up to download the
list of existing tarballs.

Change-Id: I9af310c24aa65c21cc4bd365d3df7804cba02df7

release-tarball: add libosmo-pfcp, libgtpnl

Change-Id: I4096c21352366c16167efce5c2a97f4e04c1addb