Add policy support to bonding connections

docs/examples/bonding

@@ -4,3 +4,4 @@ Connection=bond
 BindsToInterfaces=(eth0 eth2)
 IP=static
 Address="10.0.0.1/8"
+#Mode=balance-rr

docs/netctl.profile.5.txt

@@ -303,8 +303,12 @@ of the `wireless' type:
 OPTIONS FOR `bond' CONNECTIONS
 ------------------------------
 The interfaces of 'BindsToInterfaces' are bound together in the
-interface named by 'Interface'. All *ip options* are understood for
-connections of the `bond' type.
+interface named by 'Interface'. Next to the *ip options*, the following
+is understood for connections of the `bond' type:
+
+'Mode='::
+    The bonding policy. See the kernel documentation on bonding for
+    details.
 
 
 OPTIONS FOR `bridge' CONNECTIONS

src/lib/connections/bond

@@ -9,11 +9,10 @@ bond_up() {
     if is_interface "$Interface"; then
         report_error "Interface '$Interface' already exists"
         return 1
-    else
-        interface_add bond "$Interface"
     fi
-    bring_interface_up "$Interface"
 
+    interface_add bond "$Interface" "" ${Mode:+mode "$Mode"}
+    bring_interface_up "$Interface"
     for slave in "${BindsToInterfaces[@]}"; do
         ip link set dev "$slave" master "$Interface"
     done