PingApp: fix being enabled.
IPv4: Fixed proxy ARP when the next hop is the destination on the same link.
Added initial logging guidlines to misc documents.

TODO, extend and merge into INET documentation?
ARP: Added EV loglevels.
PPP: Added EV loglevels.
IPv4: Added EV loglevels.
DYMO: Added EV loglevels.
GPSR: Added EV loglevels.
Applications: Added EV loglevels.
Ethernet: Added EV loglevels.
Mobility: Added EV loglevels.
IEEE80211: Added EV loglevels.
IPv4NetworkConfigurator: Added EV loglevels.
ICMP: Added EV loglevels.
Radio: Added EV loglevels.
FSMA: Added EV loglevels.