inet6: functions shadow global variable

This renames away a variable clash:
 * ipv6_table[] is declared as a static global table;
 * ipv6_sysctl_net_init() uses ipv6_table to refer/destroy dynamic memory;
 * ipv6_sysctl_net_exit() also uses ipv6_table for the same purpose;
 * both the two last functions call kfree() on ipv6_table.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>