Fix the check for pcap_set_immediate_mode, which was failing every time.

CHANGELOG

@@ -25,10 +25,10 @@ o [NSE] Completely removed the bit.lua NSE library. All of its functions are
   replaced by native Lua bitwise operations, except for `arshift` (arithmetic
   shift) which has been moved to the bits.lua library. [Daniel Miller]
 
-o [GH#1291][GH#34] Use pcap_create instead of pcap_live_open in Nmap, and set
-  immediate mode on the pcap descriptor. This solves packet loss problems on
-  Linux and may improve performance on other platforms. [Daniel Cater, Mike
-  Pontillo, Daniel Miller]
+o [GH#1291][GH#34][GH#1339] Use pcap_create instead of pcap_live_open in Nmap,
+  and set immediate mode on the pcap descriptor. This solves packet loss
+  problems on Linux and may improve performance on other platforms.
+  [Daniel Cater, Mike Pontillo, Daniel Miller]
 
 o [GH#1150] Start host timeout clocks when the first probe is sent to a host,
   not when the hostgroup is started. Sometimes a host doesn't get probes until

configure

@@ -6418,6 +6418,9 @@ $as_echo "#define HAVE_PCAP_SET_IMMEDIATE_MODE 1" >>confdefs.h
 
 else
   # We assume our included libpcap doesn't need this check-and-define
+  # link with -lpcap for the purposes of this test
+  LIBS_OLD="$LIBS"
+  LIBS="$LIBS -lpcap"
 
   { $as_echo "$as_me:${as_lineno-$LINENO}: checking if PCAP_NETMASK_UNKNOWN is defined/handled by libpcap" >&5
 $as_echo_n "checking if PCAP_NETMASK_UNKNOWN is defined/handled by libpcap... " >&6; }
@@ -6466,6 +6469,8 @@ _ACEOF
 fi
 done
 
+  # Restore libs
+  LIBS="$LIBS_OLD"
 
 
 $as_echo "#define HAVE_LIBPCAP 1" >>confdefs.h

configure.ac

@@ -482,8 +482,13 @@ if test $have_libpcap != yes; then
   AC_DEFINE(HAVE_PCAP_SET_IMMEDIATE_MODE, 1, [Included libpcap has pcap_set_immediate_mode])
 else
   # We assume our included libpcap doesn't need this check-and-define
+  # link with -lpcap for the purposes of this test
+  LIBS_OLD="$LIBS"
+  LIBS="$LIBS -lpcap"
   PCAP_DEFINE_NETMASK_UNKNOWN
   AC_CHECK_FUNCS([pcap_set_immediate_mode])
+  # Restore libs
+  LIBS="$LIBS_OLD"
 
   AC_DEFINE(HAVE_LIBPCAP, 1, [Have libpcap library])
   LIBPCAP_LIBS="-lpcap"

nsock/src/configure

@@ -3643,6 +3643,9 @@ if test "$with_libpcap" != "no" -a "$have_libpcap" = "no"; then
 $as_echo "#define HAVE_PCAP_SET_IMMEDIATE_MODE 1" >>confdefs.h
 
 else
+  # link with -lpcap for the purposes of this test
+  LIBS_OLD="$LIBS"
+  LIBS="$LIBS -lpcap"
   for ac_func in pcap_set_immediate_mode
 do :
   ac_fn_c_check_func "$LINENO" "pcap_set_immediate_mode" "ac_cv_func_pcap_set_immediate_mode"
@@ -3654,6 +3657,8 @@ _ACEOF
 fi
 done
 
+  # Restore libs
+  LIBS="$LIBS_OLD"
 fi
 
 if test "$have_libpcap" != "no"; then

nsock/src/configure.ac

@@ -163,7 +163,12 @@ if test "$with_libpcap" != "no" -a "$have_libpcap" = "no"; then
   have_libpcap=yes
   AC_DEFINE(HAVE_PCAP_SET_IMMEDIATE_MODE, 1, [Included libpcap has pcap_set_immediate_mode])
 else
+  # link with -lpcap for the purposes of this test
+  LIBS_OLD="$LIBS"
+  LIBS="$LIBS -lpcap"
   AC_CHECK_FUNCS([pcap_set_immediate_mode])
+  # Restore libs
+  LIBS="$LIBS_OLD"
 fi
 
 if test "$have_libpcap" != "no"; then