net: Move the definition of the default Geneve udp port to public header file

Move the definition of the default Geneve udp port from the geneve
source to the header file, so we can re-use it from drivers.
Modify existing drivers to use it.

Signed-off-by: Moshe Shemesh <moshe@mellanox.com>
Reviewed-by: Or Gerlitz <ogerlitz@mellanox.com>
Cc: John Hurley <john.hurley@netronome.com>
Cc: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Acked-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>