app/testpmd: fix setting maximum packet length

app/testpmd: fix setting maximum packet length

"port config all max-pkt-len" command fails because it doesn't set the
'DEV_RX_OFFLOAD_JUMBO_FRAME' offload flag properly.

Commit in the fixes line moved the 'DEV_RX_OFFLOAD_JUMBO_FRAME' offload
flag update from 'cmd_config_max_pkt_len_parsed()' to 'init_config()'.
'init_config()' function is only called during testpmd startup, but the
flag status needs to be calculated whenever 'max_rx_pkt_len' changes.

The issue can be reproduced as [1], where the 'max-pkt-len' reduced and
'DEV_RX_OFFLOAD_JUMBO_FRAME' offload flag should be cleared but it
didn't.

Adding the 'update_jumbo_frame_offload()' helper function to update
'DEV_RX_OFFLOAD_JUMBO_FRAME' offload flag and 'max_rx_pkt_len'. This
function is called both by 'init_config()' and
'cmd_config_max_pkt_len_parsed()'.

Default 'max-pkt-len' value set to zero, 'update_jumbo_frame_offload()'
updates it to "RTE_ETHER_MTU + PMD specific Ethernet overhead" when it
is zero.
If '--max-pkt-len=N' argument provided, it will be used instead.
And with each "port config all max-pkt-len" command, the
'DEV_RX_OFFLOAD_JUMBO_FRAME' offload flag, 'max-pkt-len' and MTU is
updated.

[1]
--------------------------------------------------------------------------
dpdk-testpmd -c 0xf -n 4 -- -i --max-pkt-len=9000 --tx-offloads=0x8000
	--rxq=4 --txq=4 --disable-rss
testpmd>  set verbose 3
testpmd>  port stop all
testpmd>  port config all max-pkt-len 1518
testpmd>  port start all

// Got fail error info without this patch
Configuring Port 0 (socket 1)
Ethdev port_id=0 rx_queue_id=0, new added offloads 0x800 must be
within per-queue offload capabilities 0x0 in rte_eth_rx_queue_setup()
Fail to configure port 0 rx queues //<-- Fail error info;
--------------------------------------------------------------------------

Bugzilla ID: 625
Fixes: 761c4d66900f ("app/testpmd: fix max Rx packet length for VLAN packets")
Cc: stable@dpdk.org
Signed-off-by: Steve Yang <stevex.yang@intel.com>
Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
Acked-by: Lance Richardson <lance.richardson@broadcom.com>
Acked-by: Wisam Jaddo <wisamm@nvidia.com>
Acked-by: Xiaoyun Li <xiaoyun.li@intel.com>
Tested-by: Bo Chen <box.c.chen@intel.com>