cmdline: standardize conversion of IP address strings

cmdline: standardize conversion of IP address strings

The code to convert IPv4 and IPv6 address strings into a binary format
(inet_ntop) was included in the cmdline library because the DPDK was
historically compiled in environments where the standard inet_ntop()
function is not available. Today, this is not the case and the standard
inet_ntop() can be used.

This patch removes the internal inet_ntop*() functions and their
specific license.

There is a small functional impact: IP addresses like 012.34.56.78
are not valid anymore.

Signed-off-by: Olivier Matz <olivier.matz@6wind.com>