Border agent proxy (#1590)

* initial commit for border agent proxy

doc/spinel-protocol-src/spinel-prop-core.md

@@ -149,6 +149,8 @@ Currently defined values are:
  * 49: `CAP_ROLE_SLEEPY`
  * 52: `CAP_NET_THREAD_1_0`
  * 512: `CAP_MAC_WHITELIST`
+ * 1024: `CAP_THREAD_COMMISSIONER`
+ * 1025: `CAP_THREAD_BA_PROXY`
 
 Additionally, future capability allocations SHALL be made from the
 following allocation plan:

doc/spinel-protocol-src/spinel-tech-thread.md

@@ -254,3 +254,19 @@ When the Extended address is ommited all Devices which provided a valid PSKd are
 * Packed-Encoding: `b`
 
 Set to true to enable the native commissioner. It is mandatory before adding the joiner to the network.
+
+### PROP 5393: PROP_THREAD_BA_PROXY_ENABLED {#prop-thread-ba-proxy-enabled}
+
+* Type: Read-Write
+* Packed-Encoding: `b`
+
+Set to true to enable the border agent proxy.
+
+### PROP 5394: PROP_THREAD_BA_PROXY_STREAM {#prop-thread-ba-proxy-stream}
+
+* Type: Read-Write-Stream
+* Packed-Encoding: `dSS`
+
+Octects: | *n*  |    2    |  2
+---------|------|---------|------
+Fields:  | CoAP | locator | port