net: vmxnet: use g_new for pkt initialisation

When network transport abstraction layer initialises pkt, the maximum
fragmentation count is not checked. This could lead to an integer
overflow causing a NULL pointer dereference. Replace g_malloc() with
g_new() to catch the multiplication overflow.

Reported-by: Li Qiang <liqiang6-s@360.cn>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
Acked-by: Dmitry Fleytman <dmitry@daynix.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
