Compiled libpcap with:

./configure --host=mips --with-pcap=linux --prefix=/opt/brcm/hndtools-mipsel-uclibc

Edited the Makefile of ltraf and changed the CC:

CC=/opt/brcm/hndtools-mipsel-uclibc-3.2.3/bin/mipsel-uclibc-gcc

I also used this version of the compiled libpcap for darkstat. With darkstat I had no problems at all so far.