meta-phosphor: add ipv4/ipv6 DISTRO_FEATURES

DISTRO_FEATURES_LIBC was removed from upstream poky in 2.7 (see
ref-manual/migration.xml), and we use to get ipv4 and ipv6 picked
up as DISTRO_FEATURES as a side-effect of this variable.  It was
reported that ipv6 tools were missing from the image, so add this
back directly as a DISTRO_FEATURE.

Also, sort DISTRO_FEATURES_DEFAULT and remove any reference to the
now-deprecated DISTRO_FEATURES_LIBC.

(From meta-phosphor rev: 4877428408c6b2937c6e75d1cdb32f12ad975acf)

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Ic0d75deccf57147734849c3800b8b316a60971d0
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>