geneve: Support setting/getting source port range
Add support for geneve feature to specify source port range, see
kernel commits:
- e1f95b1992b8 ("geneve: Allow users to specify source port range")
- 5a41a00cd5d5 ("geneve, specs: Add port range to rt_link specification")
This is exactly equivalent on what is done in case of vxlan today.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>