Instead of handing over the maximum available size to the packet data
accessors, hand over a size guard that keeps track of the packets
boundaries.
This commit also moves the size-guard utilitiy header of Ping and NIC
Router to the include/net directory making it a part of the net library.
It applies the new approach to all net-lib users in the basic repositories.
Ping looses its configurability regarding the ICMP data size as this would
require an additional method in the size guard which would be used only by
Ping.
The size guard was also re-worked to fit the fact that a packet can
bring a tail as well as a header (Ethernet).
Issue #2788
The 'ping' component continuously sends ICMP Echo requests to a given IP host
and waits for the corresponding ICMP Echo replies. For each successfull ICMP
Echo handshake it prints a short statistic. By now, it can be used only with a
static IP configuration. The size of the ICMP data field can be configured. It
gets filled with the letters of the alphabet ('a' to 'z') repeatedly.
Issue #2732
