contrib: integrate RPM spec

Remove OpenSUSE bug report link, set version to @VERSION@, make it build
with CentOS 8 etc.

Related: OS#4550
Change-Id: I1d03ac87a7d0c3c600d187f3e485cb2dab8838bb

.gitignore

@@ -61,3 +61,5 @@ doc/manuals/generated/
 doc/manuals/osmomsc-usermanual.xml
 doc/manuals/common
 doc/manuals/build
+
+contrib/osmo-mgw.spec

configure.ac

@@ -209,4 +209,5 @@ AC_OUTPUT(
     doc/manuals/Makefile
     contrib/Makefile
     contrib/systemd/Makefile
+    contrib/osmo-mgw.spec
     Makefile)

contrib/osmo-mgw.spec.in

@@ -16,7 +16,7 @@
 #
 
 Name:           osmo-mgw
-Version:        1.7.0.13
+Version:        @VERSION@
 Release:        0
 Summary:        Osmocom's Media Gateway for 2G and 3G circuit-switched mobile networks
 License:        AGPL-3.0-or-later AND GPL-2.0-or-later
@@ -26,7 +26,9 @@ Source:         %{name}-%{version}.tar.xz
 BuildRequires:  automake >= 1.9
 BuildRequires:  libtool >= 2
 BuildRequires:  pkgconfig >= 0.20
+%if 0%{?suse_version}
 BuildRequires:  systemd-rpm-macros
+%endif
 BuildRequires:  pkgconfig(libosmo-netif) >= 0.6.0
 BuildRequires:  pkgconfig(libosmocore) >= 1.0.0
 BuildRequires:  pkgconfig(libosmoctrl) >= 1.1.0
@@ -88,6 +90,8 @@ make %{?_smp_mflags} check || (find . -name testsuite.log -exec cat {} +)
 
 %post   -n libosmo-mgcp-client6 -p /sbin/ldconfig
 %postun -n libosmo-mgcp-client6 -p /sbin/ldconfig
+
+%if 0%{?suse_version}
 %preun
 %service_del_preun osmo-mgw.service
 
@@ -99,6 +103,7 @@ make %{?_smp_mflags} check || (find . -name testsuite.log -exec cat {} +)
 
 %post
 %service_add_post osmo-mgw.service
+%endif
 
 %files
 %license COPYING