net: yaip: Refactor debug printing in net_if

There is now Kconfig option to enable net_if debugging.
Also use NET_DBG() instead of directly calling syslog macros
so that we can print fiber id automatically.

Change-Id: I150d363006e4be358c38308a93771ba444b0835e
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>