linux-user: netlink: add netlink neighbour emulation

linux-user: netlink: add netlink neighbour emulation

Fixes various warnings in the testsuite while building gupnp:
 gssdp-net-DEBUG: Failed to send netlink message: Operation not supported
 gupnp-context-DEBUG: Mismatch between host header and host IP (example.com, expected: 127.0.0.1)
 gupnp-context-DEBUG: Mismatch between host header and host port (80, expected 4711)
 gupnp-context-DEBUG: Mismatch between host header and host IP (192.168.1.2, expected: 127.0.0.1)
 gupnp-context-DEBUG: Mismatch between host header and host IP (fe80::01, expected: 127.0.0.1)
 gupnp-context-DEBUG: Mismatch between host header and host port (80, expected 4711)
 gupnp-context-DEBUG: Failed to parse HOST header from request: Invalid IPv6 address ?[fe80::01%1]? in URI
 gupnp-context-DEBUG: Failed to parse HOST header from request: Invalid IPv6 address ?[fe80::01%eth0]? in URI
 gupnp-context-DEBUG: Failed to parse HOST header from request: Could not parse port ?:1? in URI
 gupnp-context-DEBUG: Mismatch between host header and host IP (example.com, expected: ::1)
 gupnp-context-DEBUG: Mismatch between host header and host port (80, expected 4711)
 gupnp-context-DEBUG: Mismatch between host header and host IP (example.com, expected: ::1)
 gupnp-context-DEBUG: Mismatch between host header and host port (80, expected 4711)
 gupnp-context-DEBUG: Mismatch between host header and host IP (example.com, expected: ::1)

Signed-off-by: Helge Deller <deller@gmx.de>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>