[PATCH iproute2] ipmonitor: fix ip monitor can't work when NET_NS is not enabled

[Liping Zhang <zlpnobody@gmail.com>]

From: Liping Zhang <liping.zhang@spreadtrum.com>

In ip monitor, netns_map_init will check getnsid is supported or not.
But when /proc/self/ns/net does not exist, we just print out error
messages and exit. So user cannot use ip monitor anymore when
CONFIG_NET_NS is disabled:
  # ip monitor
  open("/proc/self/ns/net"): No such file or directory

If open "/proc/self/ns/net" failed, set have_rtnl_getnsid to false.

Fixes: d652ccbf8195 ("netns: allow to dump and monitor nsid")
Signed-off-by: Liping Zhang <liping.zhang@spreadtrum.com>
---
 ip/ipnetns.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/ip/ipnetns.c b/ip/ipnetns.c
index af87065..ccc652c 100644
--- a/ip/ipnetns.c
+++ b/ip/ipnetns.c
@@ -72,8 +72,8 @@ static int ipnetns_have_nsid(void)
 	if (have_rtnl_getnsid < 0) {
 		fd = open("/proc/self/ns/net", O_RDONLY);
 		if (fd < 0) {
-			perror("open(\"/proc/self/ns/net\")");
-			exit(1);
+			have_rtnl_getnsid = 0;
+			return 0;
 		}
 
 		addattr32(&req.n, 1024, NETNSA_FD, fd);
-- 
1.9.1