Include pdch.h in bts.h even if we're not compiling C++

bts.h needs pdch.h whether we're compiling C or C++ code so move it out
of the #ifdef.

make[1]: Entering directory '/home/daniel/scm/osmo/oc2g/osmo-pcu-oc2g/src'
  CC       osmo-bts-oc2g/oc2g_l1_if.o
In file included from osmo-bts-oc2g/oc2g_l1_if.c:39:
./bts.h:74:26: error: array type has incomplete element type ‘struct gprs_rlcmac_pdch’
  struct gprs_rlcmac_pdch pdch[8];
                          ^~~~

Change-Id: Ib39e4424f73c677b34f921917440f211e400e14f
diff --git a/src/bts.h b/src/bts.h
index ee5a692..767605c 100644
--- a/src/bts.h
+++ b/src/bts.h
@@ -38,9 +38,9 @@
 #include "gprs_ms_storage.h"
 #include "gprs_coding_scheme.h"
 #include <cxx_linuxlist.h>
-#include <pdch.h>
 #endif
 
+#include <pdch.h>
 #include <stdint.h>
 
 #define LLC_CODEL_DISABLE 0