package/aa-proxy-rs: pass board name to aa-proxy-rs at build time

Add AA_PROXY_BOARD env var to AA_PROXY_RS_CARGO_ENV, derived from
CONFIG_DIR.

Allows aa-proxy-rs to expose the Buildroot board name (e.g. aaw2b)
at runtime via option_env!("AA_PROXY_BOARD") without runtime
detection or hardcoding.

Author: manio

external/package/aa-proxy-rs/aa-proxy-rs.mk

@@ -17,7 +17,8 @@ endef
 # pass git hashes as env variables
 AA_PROXY_RS_CARGO_ENV = \
     AA_PROXY_COMMIT="$(AA_PROXY_RS_COMMIT)" \
-    BUILDROOT_COMMIT="$(BUILDROOT_COMMIT)"
+    BUILDROOT_COMMIT="$(BUILDROOT_COMMIT)" \
+    AA_PROXY_BOARD="$(notdir $(patsubst %/,%,$(CONFIG_DIR)))"
 
 # use own toolchain only for RISC-V builds (milkv-duos)
 ifeq ($(findstring milkv-duos,$(CONFIG_DIR)),milkv-duos)