Increase the memory buffer size for ssl_server2.c

Newer features in the library have increased the overall RAM usage of the
library, when all features are enabled. ssl_server2.c, with all features enabled
was running out of memory for the ssl-opt.sh test 'Authentication: client
max_int chain, server required'.

This commit increases the memory buffer allocation for ssl_server2.c to allow
the test to work with all features enabled.

programs/ssl/ssl_server2.c

@@ -1212,7 +1212,7 @@ int main( int argc, char *argv[] )
     const char *alpn_list[ALPN_LIST_SIZE];
 #endif
 #if defined(MBEDTLS_MEMORY_BUFFER_ALLOC_C)
-    unsigned char alloc_buf[100000];
+    unsigned char alloc_buf[120000];
 #endif
 
     int i;