Make socket directory configurable, don't hardcode /tmp/.xrdp

Use XRDP_SOCKET_PATH in file_loc.h

Don't define any non-socket paths in file_loc.h, they should come from
the makefiles.

Define all paths unconditionally, they should not be defined elsewhere.

Pass XRDP_SOCKET_PATH as environment variable to the backends.

xrdpapi/Makefile.am

@@ -3,6 +3,10 @@ EXTRA_DIST = \
   vrplayer.c \
   vrplayer.mk
 
+AM_CPPFLAGS = \
+  -DXRDP_SOCKET_PATH=\"${socketdir}\" \
+  -I$(top_srcdir)/common
+
 module_LTLIBRARIES = \
   libxrdpapi.la