rdma: sync some IP headers with glibc

rdma: sync some IP headers with glibc

In the commit 9a362cc71a45, new userspace header:
  (i.e rdma/rdma_user_cm.h -> linux/in6.h)
is included before the kernel space header:
  (i.e utils.h -> resolv.h -> netinet/in.h).

This leads to unsynchronous some IP headers and compiler got failure
with error: redefinition of some structs IP.

In this commit, just reorder this including to make them in-sync.

Signed-off-by: Hoang Le <hoang.h.le@dektech.com.au>
Acked-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>