bluez5: backend-native: Link with ModemManager Modem object

The Modem object provides the own number (used by +CNUM), the network
service availability and signal strength (used for the +CIND).

+CIND indicators can be activated/deactivated using AT+BIA except for
call, callsetup and callheld indicators which should always reported.
All indicators are enabled on connection.

spa/plugins/bluez5/meson.build

@@ -41,6 +41,7 @@ if get_option('bluez5-backend-hsp-native').allowed() or get_option('bluez5-backe
   endif
   if mm_dep.found()
     bluez5_deps += mm_dep
+    bluez5_sources += ['modemmanager.c']
   endif
   bluez5_sources += ['backend-native.c']
 endif