tipc: add the ability to get UDP bearer options

tipc: add the ability to get UDP bearer options

In this patch we introduce the ability to get UDP specific bearer
options such as remoteip, remoteport, localip and localport.

After some discussions on tipc-discussion on how to handle media
specific options we agreed to pass them after the media.

For media generic bearer options we already do:
$ tipc bearer get OPTION media MEDIA name|device NAME|DEVICE

For the UDP media specific bearer options we introduce in this path:
$ tipc bearer get media udp name NAME OPTION
such as
$ tipc bearer get media udp name NAME remoteip

This allows bash-completion to tab complete only appropriate options,
it makes more logical sense and it scales better. Even though it might
look a little different to the user.

In order to use the existing option parsing framework to do this we
add a flag (OPT_KEY) to the option parsing function.

If the UDP bearer has multiple remoteip addresses associated with it
(replicast) we handle the TIPC_NLA_UDP_MULTI_REMOTEIP flag and send
a TIPC_NL_UDP_GET_REMOTEIP query transparently to the user.

Signed-off-by: Richard Alpe <richard.alpe@ericsson.com>
Reviewed-by: Parthasarathy Bhuvaragan <parthasarathy.bhuvaragan@ericsson.com>
Acked-by: Jon Maloy <jon.maloy@ericsson.com>