e1000: fix multicast setting in VF

In function e1000_update_mc_addr_list_vf(), "msgbuf[0]" is used prior
to initialization at "msgbuf[0] |= E1000_VF_SET_MULTICAST_OVERFLOW".
And "msgbuf[0]" is overwritten at "msgbuf[0] = E1000_VF_SET_MULTICAST".

Fix it by moving the second line prior to the first one that mentioned
above.

Fixes: dffbaf7880a8 ("e1000: revert fix for multicast in VF")
Cc: stable@dpdk.org

Signed-off-by: Yong Wang <wang.yong19@zte.com.cn>
Acked-by: Wenzhuo Lu <wenzhuo.lu@intel.com>

Approved by: imp
Obtained from: DPDK (f58ca2f9ef6)
MFC after: 1 week

(cherry picked from commit ecf2a89a997ad4a14339b6a2f544e44b422620a0)