examples/ipsec-secgw: update required Scapy version
examples/ipsec-secgw: update required Scapy version

Update Scapy version requirement from 2.4.3rc1 to 2.4.3, which has been
used because 2.4.2 had a bug which made this version unable to install.
Accept future versions of Scapy too.

Signed-off-by: Marcin Smoczynski <490306a34ac9a546e79414e9c4162c70be9b77a9@intel.com>
Acked-by: Konstantin Ananyev <cbd5212b59ab42a210d72992d23a3aa17cfd3eaf@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk