iputils: splitting the ping6 as a package

The iputils merged the ping4 and ping6 command into the ping since the
commit ebad35fe[1], currently, iputils ping support being called using
"ping -6" or "ping6" symlinks.

In oe-core, there are two packages provide ipv6 ping, inetutils and iputils,
the inetutils-ping6 doesn't support "-I" option to bind the interface, that
cause some of scripts(e.g. LTP test[2]) which was based on iputils-ping6 fails.

If someone or a package needs iputils-ping6, they can enable it in local.conf
or add it into rdepends directly.

Ref:
[1] https://github.com/iputils/iputils/commit/e3de851b809c7b72ccc654a72b6af61d
[2] https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/

 \
    containers/netns/netns_comm.sh#L25

Signed-off-by: Xiangyu Chen <xiangyu.chen@windriver.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>