net: icmp: Don't report error on ICMP messages w/o handler

ICMPv4/6 modules print error when ICMP message handling fails, which
includes no message handler registered. This is a bit problematic, as
there are many ICMP messages that Zephyr does not process, and every
time such a message is received, an error log is printed (which wasn't
the case before ICMP rework).

Restore the old behavior (no log on unrecognized ICMP message) by
explicitly filtering out ENOENT error code from printing error. That
way, log will only be printed if an error occured within the actual
message handler.

Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>