examples/ip_fragmentation: support big packets

examples/ip_fragmentation: support big packets

In some vendors the RX and TX configuration must be the same, therefore
the MTU size need to be equal to max_rx_pkt_len.
The MTU is the largest size packet in bytes that can be sent on the
network, therefore before changing this parameter, the NIC could not
receive packets larger than 1500 bytes, which is the default MTU size.
In addition, scatter-gather need to be enabled in order to receive
frames bigger than mbuf size.

Signed-off-by: Noa Ezra <noae@mellanox.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>