ppp: add missing -fPIC to rp-pppoe.so CFLAGS

Fixes build error with LTO

Signed-off-by: Felix Fietkau <nbd@nbd.name>

package/network/services/ppp/patches/203-opt_flags.patch

@@ -30,3 +30,14 @@ Signed-off-by: Jo-Philipp Wich <jo@mein.io>
  OBJS = pppdump.o bsd-comp.o deflate.o zlib.o
  
  INSTALL= install
+--- a/pppd/plugins/rp-pppoe/Makefile.linux
++++ b/pppd/plugins/rp-pppoe/Makefile.linux
+@@ -39,7 +39,7 @@ debug.o: debug.c
+ 	$(CC) $(CFLAGS) -c -o debug.o debug.c
+ 
+ rp-pppoe.so: plugin.o discovery.o if.o common.o
+-	$(CC) $(CFLAGS) -o rp-pppoe.so -shared plugin.o discovery.o if.o common.o
++	$(CC) $(CFLAGS) -fPIC -o rp-pppoe.so -shared plugin.o discovery.o if.o common.o
+ 
+ install: all
+ 	$(INSTALL) -d -m 755 $(LIBDIR)