gtp: fix missing initialization of netns file descriptor

0 is a valid file descriptor and it is the default value after calloc(),
so set this -1 so we don't send it through netlink as used init_netns.

Fixes: 200b2f4 ("gtp-rtnl: and netns support")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
1 file changed