ila: remove unused macro 'ILA_HASH_TABLE_SIZE'

net/ipv6/ila/ila_xlat.c:604:0: warning: macro "ILA_HASH_TABLE_SIZE" is not used [-Wunused-macros]

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>