rename netcat.c to netcat_main.c

In order to split out the build to multiple object files (one per track)
the main source file needs to be renamed.

Signed-off-by: Philipp A. Hartmann <pah@qo.cx>
rename track files to *.c (to prepare separate build)

In order to easy review of the changes, this commit just
renames the trk?.h files to trk?.c, while still including
them from netcat_main.c.

Signed-off-by: Philipp A. Hartmann <pah@qo.cx>
split out tracks to individual object files

In order to reduce the memory requirements for building the
kernel module, build each track into an object file individually.

For this purpose, each "track object" exports the data array and its
length explicitly, which can then be used from netcat_main.c.

Signed-off-by: Philipp A. Hartmann <pah@qo.cx>
add struct netcat_track to store track information

The individual track object now simply export a struct netcat_track
with .name, .len, and .data members.

Signed-off-by: Philipp A. Hartmann <pah@qo.cx>
replaced hard-coded number of tracks with sizeof

This replaces the hard-coded '6' with the usual sizeof magic, which is
an important improvement to ease further releases with a different
number of tracks ;-)

Cherry-picked and squashed from #28

Signed-off-by: Philipp A. Hartmann <pah@qo.cx>
move external track symbols to netcat.h

Extern symbols are frowned upon in .c files.

Signed-off-by: Philipp A. Hartmann <pah@qo.cx>
Merge branch 'multiple-objects' of https://github.com/pah/netcat-cpi-kernel-module

Modified slightly to correct and include path error that prevented compiling.

Conflicts:
	netcat_main.c