debian: define SPEED_UNKNOWN if missing in linux/ethtool.h

Debian's version of linux/ethtool.h seems to be outdated
and does not contain define SPEED_UNKNOWN, fix this by a
manual define.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
debian: compile fix for programs using ncurses

For some reason the Debian ncurses version does not
contain a ncurses.pc pkg-config file.

Fix this by echoing "-lncurses" if the command fails:
 pkg-config --libs ncurses

This fix will make ifpps compile on Debian Squeeze 6.0.8.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>