Convert `InfoBond::XmitHashPolicy(u8)` to enum

[cathay4t]

const BOND_XMIT_POLICY_LAYER2: u8 = 0;
const BOND_XMIT_POLICY_LAYER34: u8 = 1;
const BOND_XMIT_POLICY_LAYER23: u8 = 2;
const BOND_XMIT_POLICY_ENCAP23: u8 = 3;
const BOND_XMIT_POLICY_ENCAP34: u8 = 4;
const BOND_XMIT_POLICY_VLAN_SRCMAC: u8 = 5;