To support multiple nlmon sources, move the logic that reads from iwmon
device into main.c instead of nlmon. nlmon.c now becomes agnostic of
how the packets are actually obtained. Packets are fed in via
high-level APIs such as nlmon_print_rtnl, nlmon_print_genl,
nlmon_print_pae.
The -F option is undocumented but allows you to pass a nl80211
family ID so iwmon doesn't ignore messages which don't match the
systems nl80211 family ID (i.e. pcaps from other systems).
This is somewhat of a pain to use since its unclear what the other
system's family ID actually is until you run it though something
like wireshark. Instead iwmon can ignore the family ID when in
read mode which makes reading other systems pcap files automatic.
Expand nlmon_create to be useful for both pcaps and monitoring. Doing
this also lets iwmon filter pcaps based on --no-ies,rtnl,scan etc
flags since they are part of the config.
Commit c7640f8346 was meant to fix a sign compare warning
in clang because NLMSG_NEXT internally compares the length
with nlmsghdr->nlmsg_len which is a u32. The problem is the
NLMSG_NEXT can underflow an unsigned value, hence why it
expects an int type to be passed in.
To work around this we can instead pass a larger sized
int64_t which the compiler allows since it can upgrade the
unsigned nlmsghdr->nlmsg_len. There is no underflow risk
with an int64_t either because the buffer used is much
smaller than what can fit in an int64_t.
Fixes: c7640f8346 ("monitor: fix integer comparison error (clang)")
To help understand scanning results a bit better and cut down on scan
output add an option to not print the contents of the IEs. Only the
SSID IE will be printed.
