ip fou: Support binding FOU ports

ip fou: Support binding FOU ports

This patch adds support for binding FOU ports using iproute2.
Kernel-support was added in 1713cb37bf67 ("fou: Support binding FoU
socket").

The parse function now handles new arguments for setting the
binding-related attributes, while the print function writes the new
attributes if they are set. Also, the man page has been updated.

v2->v3:
* Remove redundant ll_init_map()-calls (thanks David Ahern).

v1->v2 (all changes suggested by David Ahern):
* Fix reverse Christmas tree ordering.
* Remove redundant peer_port_set-variable, it is enough to check
peer_port.
* Add proper error handling of invalid local/peer addresses.
* Use interface name and not index.
* Remove updating fou-header file, it is already done.

Signed-off-by: Kristian Evensen <kristian.evensen@gmail.com>
Signed-off-by: David Ahern <dsahern@gmail.com>