Add dnsmasq to machines with role bsc, not only sysmocom-bsc-image

This way we have it too in sysmocom-nitb-image, but only when needed,
that is: when we build for a machine inheritinh from sysmocom-bsc, which
is a machine not containing any BTS HW and thus requires a BTS connected
to it, so it needs a DNS server to serve it.

conf/machine/sysmocom-bsc.conf

@@ -1 +1,5 @@
 MACHINEOVERRIDES = "${MACHINE}:sysmocom-bsc"
+
+MACHINE_EXTRA_RDEPENDS = "\
+	dnsmasq \
+	"

recipes-apps/images/sysmocom-bsc-image.bb

@@ -1,6 +1,6 @@
 require sysmocom-image.inc
 
-IMAGE_INSTALL_append = " task-sysmocom dnsmasq "
+IMAGE_INSTALL_append = " task-sysmocom "
 
 # This variant of the image will run osmo-bts and osmo-bsc
 activate_bsc() {