Check for _USE_TIRPC_IPV6 while parsing and using netconf
 entries

/etc/netconfig on Freebsd has the following order:
udp6       tpi_clts      v     inet6    udp     -       -
tcp6       tpi_cots_ord  v     inet6    tcp     -       -
udp        tpi_clts      v     inet     udp     -       -
tcp        tpi_cots_ord  v     inet     tcp     -       -
rawip      tpi_raw       -     inet      -      -       -
local      tpi_cots_ord  -     loopback  -      -       -

Currently, tirpc only checks for the type of entries provided,
i.e. udp or tcp. Both inet and inet6 families of entries are
parsed without checking _USE_TIRPC_IPV6. This causes a mismatch
error when Ganesha tries to configure udp but udp6's entry is
parsed and returned. This check is not necessary in linux as
inet family entries are enumerated before inet6 entries.

Signed-off-by: Viji Ganapathi <vganapathi@panasas.com>
Signed-off-by: Matt Benjamin <matt@linuxbox.com>