mavlink: enable partner ip status print

[jnippula]

Enable partner IP to be printed in mavlink status output also other than POSIX (SITL) build

Example:

instance #1:
        mavlink chan: #1
        type:           GENERIC LINK OR RADIO
        flow control: OFF
        rates:
          tx: 1246.4 B/s
          txerr: 0.0 B/s
          tx rate mult: 1.000
          tx rate max: 1000000 B/s
          rx: 0.0 B/s
          rx loss: 0.0%
        FTP enabled: YES, TX enabled: YES
        mode: Normal
        Forwarding: Off
        MAVLink version: 1
        transport protocol: UDP (14541, remote port: 12345)
        Broadcast enabled: NO
        Multicast enabled: NO
        partner IP: 192.168.200.100
saluki>