bnxt_en: Add a driver specific gre_ver_check devlink parameter.

This patch adds following driver-specific permanent mode boolean
parameter.

gre_ver_check - Generic Routing Encapsulation(GRE) version check
will be enabled in the device. If disabled, device skips version
checking for GRE packets.

Cc: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: Vasundhara Volam <vasundhara-v.volam@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>