nmap hasn't worked properly on AIX for a while (since it started using dnet), 
these patches fix that.

configure.in
AC_CHECK_HEADERS - some of the headers require sys/socket.h be included first.

Move the check for ac_cv_header_sys_ndd_var_h before the others so that ndd is 
used on AIX.


src/route-bsd.c
Make it work on AIX using getkerninfo(KINFO_RT_DUMP,...).

src/eth-ndd.c
Setting ETH_TYPE_IP caused the bind() to fail with EEXIST, removing that 
appears to work.
Fill in e->device
nmap calls eth_send with a length less than the minimum length for an ethernet 
packet which causes write to fail with EMSGSIZE (Message too long says 
strerror(), but really is too short), so we pad it.
No point in looping once we have an answer.