build: Use $(MAKE) instead of `make`.

On some systems (FreeBSD) `make` is named `gmake` and using
`make` in the Makefile breaks the build. The correct way of
calling make inside a Makefile is to use `$(MAKE)` variable.

This fixes distclean and README.build targets. Reported by kraiv.

git-svn-id: http://streamboard.de.vu/svn/oscam/trunk@8474 4b0bc96b-bc66-0410-9d44-ebda105a78c1
Use IPPROTO_TCP instead of SOL_TCP for cross-platform compatibility.

Modern Linux tcp(7) man page doesn't even mention SOL_TCP. The
correct and portable way is to use IPPROTO_TCP.

This fixes compilation of FreeBSD. Reported by kraiv.

git-svn-id: http://streamboard.de.vu/svn/oscam/trunk@8475 4b0bc96b-bc66-0410-9d44-ebda105a78c1