libteam: set netlink event socket as non-blocking
libteam: set netlink event socket as non-blocking

In some situations it was observed that recvmsg() blocks even if
epoll_wait() reports the netlink socket as ready:

 select(15, [3 9 10 14], [], [], NULL)   = 1 (in [9])
 epoll_wait(9, [{EPOLLIN, {u32=8, u64=8}}], 2, -1) = 1
 recvmsg(8,                                  ### blocked

(9 is the epoll fd, 8 the nl_cli event socket).

Probably this is caused by a bug in kernel, however it seems more
robust anyway to set the socket as non-blocking to avoid problems like
this.

Signed-off-by: Beniamino Galvani <76686399b73357bbab3cce10937c280c528b17ce@redhat.com>
Signed-off-by: Jiri Pirko <1b548d10035ae428195c41f5d55eedb1437ccd8a@mellanox.com>

jpirko/libteam,jpirko/libteam,jpirko/libteam