Include ssl_misc.h for additional SSL helper files

This commit replaces #include "common.h" in favour of #include
"ssl_misc.h".

Signed-off-by: Harry Ramsey <harry.ramsey@arm.com>
diff --git a/library/net_sockets.c b/library/net_sockets.c
index ef89a88..33616bc 100644
--- a/library/net_sockets.c
+++ b/library/net_sockets.c
@@ -15,7 +15,7 @@
 #define _XOPEN_SOURCE 600 /* sockaddr_storage */
 #endif
 
-#include "common.h"
+#include "ssl_misc.h"
 
 #if defined(MBEDTLS_NET_C)