igb: fix ieee1588 timestamping
igb: fix ieee1588 timestamping

Ieee1588 reads system time to set its timestamp. On 1G NICs, for example,
i350, system time is disabled by default. It means the ieee1588 timestamp
will always be 0.
This patch enables system time when ieee1588 is enabled.

Signed-off-by: Wenzhuo Lu <58cb9036bdff9a5412edc3b9f70e105ccf59954f@intel.com>
Acked-by: John McNamara <af31595c36a4239b9676e9b3a777d3e2f15a6c4d@intel.com>

tsphillips/dpdk-fork,tsphillips/dpdk-fork,mixja/dpdk,msune/dpdk,tsphillips/dpdk-fork,msune/dpdk,mixja/dpdk,venkynv/dpdk-mirror,john-mcnamara-intel/dpdk,venkynv/dpdk-mirror,msune/dpdk,john-mcnamara-intel/dpdk,mixja/dpdk,mixja/dpdk,john-mcnamara-intel/dpdk,tsphillips/dpdk-fork,venkynv/dpdk-mirror,venkynv/dpdk-mirror,msune/dpdk,john-mcnamara-intel/dpdk