ip: Fixed build issue

ip: Fixed build issue

ipnetns.c:47:12: error: static declaration of 'setns' follows non-static
declaration
[ 16s] static int setns(int fd, int nstype)
[ 16s] ^~~~~
[ 16s] In file included from /usr/include/sched.h:43:0,
[ 16s] from ipnetns.c:11:
[ 16s] /usr/include/bits/sched.h:92:12: note: previous declaration of 'setns' was here
[ 16s] extern int setns (int __fd, int __nstype) __THROW;
[ 16s] ^~~~~
[ 16s] : recipe for target 'ipnetns.o' failed
[ 16s] make[1]: *** [ipnetns.o] Error 1

Change-Id: Ifdb58bf38b6800bcd4f2e2c7d9a0a87c7e60f418
Signed-off-by: Saurav Babu <saurav.babu@samsung.com>