dbus: allow firewalld to communicate with NetworkManager

Usually, this "<allow send_destination="..."/>" part is shipped
by firewalld's D-Bus policy. However, if firewalld is initially
not installed with NetworkManager already running, dbus-daemon
seems to cache the missing permission for the D-Bus connection.
As a result, when installing and starting firewalld, NetworkManager
requests fail until restart:

  firewall: [0x7f4b83643890,change:"eth1"]: complete: request failed (Rejected send message, 1 matched rules; type="method_call", sender=":1.3" (uid=0 pid=715 comm="/usr/sbin/NetworkManager --no-daemon ") interface="org.fedoraproject.FirewallD1.zone" member="changeZone" error name="(unset)" requested_reply="0" destination=":1.25" (uid=0 pid=1243 comm="/usr/bin/python -Es /usr/sbin/firewalld --nofork -"))

https://bugzilla.redhat.com/show_bug.cgi?id=1436770

src/org.freedesktop.NetworkManager.conf

@@ -27,6 +27,8 @@
                 <allow send_destination="org.freedesktop.NetworkManager.strongswan"/>
                 <allow send_interface="org.freedesktop.NetworkManager.VPN.Plugin"/>
 
+                <allow send_destination="org.fedoraproject.FirewallD1"/>
+
                 <!-- Allow the custom name for the dnsmasq instance spawned by NM
                      from the dns dnsmasq plugin to own it's dbus name, and for
                      messages to be sent to it.