datapath: Fix IP ID setting.

datapath: Fix IP ID setting.

Eliminate the extra call to ip_select_ident(), and place the
__ip_select_ident() call where the ip_select_ident() call was.
This fixes two problems: Before, the call to ip_select_ident() did
always zero out the value set earlier by __ip_select_ident().  Also,
when __ip_select_ident() was called before setting the iph->daddr,
ident calculation was possibly based on uninitialized data (but as
the result was masked by the later call to ip_select_ident() it was
not visible).

Signed-off-by: Jarno Rajahalme <jarno.rajahalme@nsn.com>
Signed-off-by: Jesse Gross <jesse@nicira.com>