IP Flow Hash Config fixes

IP Flow Hash Config fixes

- the flow hash config is (and was) cached on the load-balance object so the fib_table_t struct is not used a switch time. Therefore changes to the table's flow hash config need to be propagated to all load-balances and hance all FIB entries in the table.
- enable API for setting the IPv6 table flow hash config
- use only the hash config in the fib_table_t object and not on the ipX_fib_t
- add tests.

Change-Id: Ib804c11162c6d4972c764957562c372f663e05d4
Signed-off-by: Neale Ranns <nranns@cisco.com>