bumped stack to 3k (not sure we needed to), cleaned up old serdes test

bumped stack to 3k (not sure we needed to), cleaned up old serdes test
code: eth_serdes.c and serdes_txrx.c, can tx over serdes at interp 4
(underruns quite frequently), same behavior as regular txrx.c

git-svn-id: http://gnuradio.org/svn/gnuradio/trunk@10291 221aa14e-8319-0410-a670-987f0aec2ac5