Add missing bond hash policy VLAN_SRCMAC

[lorenz]

Linux added a new bond transmit hashing policy, VLAN_SRCMAC in [1], available since Linux 5.12. Add this hashing policy into the respective data structures.

[1] https://github.com/torvalds/linux/commit/7b8fc0103bb51d1d3e1fb5fd67958612e709f883