net: avoid using variable length array in net_client_init()

net: avoid using variable length array in net_client_init()

net_client_init() uses a variable length array to store the prefix
of 'ipv6-net' parameter (e.g. if ipv6-net=fec0::0/64, the prefix
is 'fec0::0').
This patch introduces g_strsplit() to split the 'ipv6-net' parameter,
so we can remove the variable length array.

Suggested-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>