When HAVE_SETNS is not set, iproute2 provides a local implementation of this
function based on __NR_setns.
This macro is defined in sys/syscall.h, which was not included, thus the local
implementation always returned -1.
CC: Vadim Kochan <vadim4j@gmail.com> Fixes: eb67e4498aec ("lib: Add netns_switch func for change network namespace") Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>