convert -idirafter to -I

The local include trees no longer need -idirafter semantics, so use the
normal -I flags to avoid random cruft on users' systems.  This fixes Gentoo
#283759 where user had local headers named the same as the net-tools local
headers, but the toolchain defaulted to the system paths due to -idirafter.

Makefile

@@ -112,7 +112,7 @@ endif
 
 NET_LIB = $(NET_LIB_PATH)/lib$(NET_LIB_NAME).a
 
-CPPFLAGS += -I. -idirafter ./include/ -I$(NET_LIB_PATH)
+CPPFLAGS += -I. -I$(TOPDIR)/include -I$(NET_LIB_PATH)
 LDFLAGS  += -L$(NET_LIB_PATH)
 
 SUBDIRS	= man/ $(NET_LIB_PATH)/

lib/Makefile

@@ -36,7 +36,7 @@ OBJS	= $(sort $(VARIA) $(AFOBJS) $(HWOBJS) \
 
 # This can be overwritten by the TOPLEVEL Makefile
 TOPDIR=..
-CFLAGS += -I$(TOPDIR) -idirafter $(TOPDIR)/include # -fPIC
+CFLAGS += -I$(TOPDIR) -I$(TOPDIR)/include # -fPIC
 SONAME=libnet-tools.so.0
 
 .SUFFIXES: .a .so