package/mbedtls: add configurable DTLS-SRTP support

Add a new option to have MbedTLS builds that support DTLS-SRTP.
We can only enable the support, it's disabled by default.

Signed-off-by: Dmitry Ilyin <dima@doty.ru>
[yann.morin.1998@free.fr:
  - rename variable
  - fix variable name in .mk
  - drop unnecessary ref to AWS library
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/mbedtls/Config.in

@@ -29,4 +29,10 @@ config BR2_PACKAGE_MBEDTLS_COMPRESSION
 	  sure CRIME and similar attacks are not applicable to your
 	  particular situation.
 
+config BR2_PACKAGE_MBEDTLS_DTLS_SRTP
+	bool "enable DTLS-SRTP support"
+	help
+	  Enable support for negotiation of DTLS-SRTP (RFC 5764)
+	  through the use_srtp extension.
+
 endif

package/mbedtls/mbedtls.mk

@@ -72,4 +72,12 @@ else ifeq ($(BR2_microblaze)$(BR2_MIPS_CPU_MIPS32R6)$(BR2_MIPS_CPU_MIPS64R6),y)
 MBEDTLS_POST_CONFIGURE_HOOKS += MBEDTLS_DISABLE_ASM
 endif
 
+ifeq ($(BR2_PACKAGE_MBEDTLS_DTLS_SRTP),y)
+define MBEDTLS_ENABLE_DTLS_SRTP
+	$(SED) "s://#define MBEDTLS_SSL_DTLS_SRTP:#define MBEDTLS_SSL_DTLS_SRTP:" \
+		$(@D)/include/mbedtls/config.h
+endef
+MBEDTLS_POST_PATCH_HOOKS += MBEDTLS_ENABLE_DTLS_SRTP
+endif
+
 $(eval $(cmake-package))