The function get_net_ns_by_pid(), to get a network
namespace from a pid_t, will be required in cfg80211
as well. Therefore, let's move it to net_namespace.c
and export it. We can't make it a static inline in
the !NETNS case because it needs to verify that the
given pid even exists (and return -ESRCH).
Signed-off-by: NJohannes Berg <johannes@sipsolutions.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>