40network: check for brctl

if a bridge is configured on the kernel command line and brctl is
missing call die()

modules.d/40network/parse-bond.sh

@@ -18,6 +18,7 @@ if getarg bond= >/dev/null ; then
     if [ -z "$netroot" ] ; then
         die "No netboot configured, bond is invalid"
     fi
+    command -v brctl >/dev/null 2>&1 || die "No 'brctl' installed"
 fi
 
 # We translate list of slaves to space-separated here to mwke it easier to loop over them in ifup

modules.d/40network/parse-bridge.sh

@@ -16,6 +16,7 @@ if getarg bridge= >/dev/null ; then
     if [ -z "$netroot" ] ; then
         die "No netboot configured, bridge is invalid"
     fi
+    command -v brctl >/dev/null 2>&1 || die "No 'brctl' installed" 
 fi
 
 parsebridge() {