After these patches, the iproute2 name of netns is displayed instead of
the nsid. It's easier to read/understand.

v1 -> v2:
 - open netns socket and init netns map only when needed

 ip/ip_common.h |  3 +++
 ip/ipaddress.c | 20 +++++++++++++++-----
 ip/iplink.c    | 18 ++++++++++++++++--
 ip/ipnetns.c   | 22 ++++++++++++++++++++--
 4 files changed, 54 insertions(+), 9 deletions(-)
 
Comments are welcomed, 
Regards, 
Nicolas