Use BSD headers for ICMP portability.

diff --git a/configure.in b/configure.in
index 95ed29f..9167e3e 100644
--- a/configure.in
+++ b/configure.in
@@ -507,6 +507,10 @@
   AC_DEFINE(NO_REENTRANT_X11)
 fi
 
+dnl **** Check for endianness ****
+
+AC_C_BIGENDIAN
+
 dnl **** Check for functions ****
 
 AC_FUNC_ALLOCA()