xl2tpd: update source, import some useful patches

Yousong Zhou <yszhou4tech@gmail.com> made a couple of useful fixes
mostly for the xl2tpd-control tool which was broken.
imported them (patches/2*) here.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

net/xl2tpd/patches/120-no-bsd-signal-in-musl.patch

@@ -1,7 +1,5 @@
-Index: xl2tpd-1.3.6/xl2tpd.c
-===================================================================
---- xl2tpd-1.3.6.orig/xl2tpd.c
-+++ xl2tpd-1.3.6/xl2tpd.c
+--- a/xl2tpd.c
++++ b/xl2tpd.c
 @@ -30,7 +30,7 @@
  #include <errno.h>
  #include <unistd.h>