ethdev: add default value for max segment

rte_eth_dev_info structure exposes, nb_seg_max & nb_mtu_seg_max
to provide maximum number of supported segments for a given platform.

Defining UINT16_MAX as default value of above mentioned variables to
expose support of infinite/maximum segments.

Based on above values, application can decide best size for buffers
while creating mbuf pool.

Signed-off-by: Sunil Kumar Kori <skori@marvell.com>
Acked-by: Andrew Rybchenko <arybchenko@solarflare.com>