FS-11659 [core] Fix implicit declaration of RAND_bytes

Since the update to openssl-1.1.1a the compile fails like this:

  CC       src/libfreeswitch_la-switch_rtp.lo
src/switch_rtp.c: In function 'switch_rtp_get_random':
src/switch_rtp.c:2419:2: error: implicit declaration of function 'RAND_bytes'; did you mean 'RSA_bits'? [-Werror=implicit-function-declaration]
  RAND_bytes(buf, len);
  ^~~~~~~~~~
  RSA_bits
cc1: all warnings being treated as errors
make[4]: *** [Makefile:2377: src/libfreeswitch_la-switch_rtp.lo] Error 1

This patch adds the missing include.
Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>

src/include/switch_ssl.h

@@ -38,6 +38,7 @@
 #endif
 #include <openssl/crypto.h>
 #include <openssl/pem.h>
+#include <openssl/rand.h>
 #include <openssl/conf.h>
 #include <openssl/x509v3.h>
 #ifndef OPENSSL_NO_ENGINE