clean up makefile

Change the makefile a bit to add the optional
things in a cleaner way.
makefile: don't include .config

This is no longer used to configure the tool.
makefile: allow passing NO_PKG_CONFIG

To build iw without pkg-config, you can now do something
like

$ make NO_PKG_CONFIG=1 LDFLAGS=-lnl
add Android build system

Unfortunately Android's libnl doesn't have nla_put_flag()
so add a simple source file to declare that for now.
iw/event: Print out PROBE_CLIENT event information.

For instance:
vap0 (phy #0): probe client 00:ab:cd:ef:03:5c (cookie f54bb400): no ack

Signed-off-by: Ben Greear <greearb@candelatech.com>
iw:  Support can_scan_one flag.

Signed-off-by: Ben Greear <greearb@candelatech.com>
Fix compile on systems that don't have htole16.

Use htons and manual tweaking to get it right.

Signed-off-by: Ben Greear <greearb@candelatech.com>