Add icmp-ip example with inet_ip decoder

[bobrik]

Example metrics from local pings:

ivan@vm:~$ curl -s http://localhost:9435/metrics | fgrep ebpf_exporter_icmp
# HELP ebpf_exporter_icmp4_received_packets_total Number of icmp packets received over IPv4
# TYPE ebpf_exporter_icmp4_received_packets_total counter
ebpf_exporter_icmp4_received_packets_total{source_addr="10.2.0.15"} 4
ebpf_exporter_icmp4_received_packets_total{source_addr="127.0.0.1"} 6
# HELP ebpf_exporter_icmp6_received_packets_total Number of icmp packets received over IPv6
# TYPE ebpf_exporter_icmp6_received_packets_total counter
ebpf_exporter_icmp6_received_packets_total{source_addr="::1"} 4
ebpf_exporter_icmp6_received_packets_total{source_addr="fe80::5054:ff:fe12:3456"} 4
ebpf_exporter_icmp6_received_packets_total{source_addr="fec0::5054:ff:fe12:3456"} 6

[cdkunsong]

hi, @bobrik
I also want to discuss a issue, whether it is possible to use struct type for value,
although I see in tcp-window-clamps.bpf.c
tcp_rmem_schedule_enters
__type(value, struct sock *);
but it don't use by metrics .
Currently, it seems that a struct type cannot be supported, and it can parse multiple member values.

Can you explain this problem, thanks!

[bobrik]

@cdkunsong, could you open a new issue describing what you're trying to do?

[cdkunsong]

#253
I have create new issue.