net/icpmv4: Add dynamically registered ICMPv4 handlers

As it is done for ICMPv6. This will prove to be useful for implementing
an echo reply handler in a ping for instance.

Change-Id: I969a1da60f2a4ea59eee5c9983eb6e340923e2ef
Signed-off-by: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>