datapath: Use alternate name for udp_sock_create() backport

datapath: Use alternate name for udp_sock_create() backport

Account for kernels which provide udp_sock_create() in an
insufficient version.

Avoids the following error when inserting openvswitch.ko on
respective kernels:

openvswitch: exports duplicate symbol udp_sock_create (owned by udp_tunnel)

Fixes: eb6eebd28 ("datapath: Account for "udp: Add udp_sock_create for UDP tunnels to open listener socket")
Signed-off-by: Thomas Graf <tgraf@noironetworks.com>
Cc: Jesse Gross <jesse@nicira.com>
Acked-by: Jesse Gross <jesse@nicira.com>