ngcp-services-ce: add alternative depends on bsd-mailx to make lintian happy

Make lintian happy WRT:

  ngcp-services-ce: virtual-package-depends-without-real-package-depends depends: mailx

From: Michael Prokop <mprokop@sipwise.com>

debian/control

@@ -70,7 +70,7 @@ Description: Metapackage for NGCP platform services
 
 Package: ngcp-services-ce
 Architecture: all
-Depends: ${shlibs:Depends}, ${misc:Depends}, kamailio, kamailio-mysql-modules, kamailio-xml-modules, percona-server-client-5.1, percona-server-server-5.1, ntp, rsyslog-mysql, ngcp-mediaproxy-ng, ngcp-asterisk, ngcp-cdr-exporter, ngcp-mediator, ngcp-ossbss-apache, ngcp-ossbss-billing, ngcp-ossbss-common, ngcp-ossbss-voip, ngcp-ossbss-system, ngcp-ossbss-xmldispatcher, ngcp-reminder, ngcp-sems, ngcp-www-admin, ngcp-www-csc, ngcp-rate-o-mat, ngcp-vmnotify, ngcp-check-tools, ngcp-system-tools-ce, ngcp-rsyslog-tools, ngcp-cleanup-tools, mailx, ssh, bzip2, python
+Depends: ${shlibs:Depends}, ${misc:Depends}, kamailio, kamailio-mysql-modules, kamailio-xml-modules, percona-server-client-5.1, percona-server-server-5.1, ntp, rsyslog-mysql, ngcp-mediaproxy-ng, ngcp-asterisk, ngcp-cdr-exporter, ngcp-mediator, ngcp-ossbss-apache, ngcp-ossbss-billing, ngcp-ossbss-common, ngcp-ossbss-voip, ngcp-ossbss-system, ngcp-ossbss-xmldispatcher, ngcp-reminder, ngcp-sems, ngcp-www-admin, ngcp-www-csc, ngcp-rate-o-mat, ngcp-vmnotify, ngcp-check-tools, ngcp-system-tools-ce, ngcp-rsyslog-tools, ngcp-cleanup-tools, bsd-mailx | mailx, ssh, bzip2, python
 Conflicts: ngcp-services-pro
 Description: Metapackage for NGCP platform services
  This metapackage installs the required services in a NGCP