[ncp] Transforming spinel frames between AP and NCP (#2402)

* [ncp] Transforming spinel frames between AP and NCP

NCP Spinel Transformer allows to transform spinel frames sent between
Application Processor (AP) and Network Co-Processor (NCP).

Spinel frames can be transformed by using transformer library
(or libraries) implementing spinel_transformer.hpp. Libraries
can be specified using option --with-ncp-spinel-transformer-libs.
Addidionaly, transformer's outbound buffer can be changed if needed,
using option --with-ncp-spinel-transformer-outbound-buffer-size.

examples/apps/ncp/Makefile.am

@@ -63,6 +63,12 @@ LDADD_COMMON                                                          += \
     $(NULL)
 endif
 
+if OPENTHREAD_ENABLE_NCP_SPINEL_ENCRYPTER
+LDADD_COMMON                                                          += \
+    $(OPENTHREAD_NCP_SPINEL_ENCRYPTER_LIBS)                              \
+    $(NULL)
+endif # OPENTHREAD_ENABLE_NCP_SPINEL_ENCRYPTER
+
 if OPENTHREAD_ENABLE_NCP_FTD
 bin_PROGRAMS                                                          += \
     ot-ncp-ftd                                                           \