DHCPv6: Fix a potential buffer overflow reading NA/TA addresses
DHCPv6: Fix a potential buffer overflow reading NA/TA addresses

Only copy upto the size of the address option rather than the
option length.

Found by Maxime Villard <max@m00nbsd.net>

rsmarples/dhcpcd,rsmarples/dhcpcd,rsmarples/dhcpcd