app/testpmd: set and clear keep CRC offload flag

app/testpmd: set and clear keep CRC offload flag

If the "port config all crc-strip on" command is issued,
The DEV_RX_OFFLOAD_KEEP_CRC offload flag should be cleared.

If the "port config all crc-strip off command is issued,
The DEV_RX_OFFLOAD_KEEP_CRC offload flag should be set.

Fixes: 70815c9ecadd ("ethdev: add new offload flag to keep CRC")
Signed-off-by: Bernard Iremonger <bernard.iremonger@intel.com>
Acked-by: Andrew Rybchenko <arybchenko@solarflare.com>