Make some CLIENTHELLO_MSG function arguments const

There were a few places where they could be declared const so this commit
does that.
Reviewed-by: NKurt Roeckx <kurt@openssl.org>
Reviewed-by: NRich Salz <rsalz@openssl.org>

ssl/ssl_locl.h

@@ -2058,7 +2058,7 @@ __owur int dtls1_process_heartbeat(SSL *s, unsigned char *p,
 
 __owur int tls_get_ticket_from_client(SSL *s, CLIENTHELLO_MSG *hello,
                                       SSL_SESSION **ret);
-__owur int tls_check_client_ems_support(SSL *s, CLIENTHELLO_MSG *hello);
+__owur int tls_check_client_ems_support(SSL *s, const CLIENTHELLO_MSG *hello);
 
 __owur int tls12_get_sigandhash(WPACKET *pkt, const EVP_PKEY *pk,
                                 const EVP_MD *md);

ssl/t1_lib.c

@@ -1701,7 +1701,7 @@ static int tls1_alpn_handle_client_hello_late(SSL *s, int *al)
  * Sadly we cannot differentiate 10.6, 10.7 and 10.8.4 (which work), from
  * 10.8..10.8.3 (which don't work).
  */
-static void ssl_check_for_safari(SSL *s, CLIENTHELLO_MSG *hello)
+static void ssl_check_for_safari(SSL *s, const CLIENTHELLO_MSG *hello)
 {
     unsigned int type;
     PACKET sni, tmppkt;
@@ -2905,7 +2905,7 @@ int tls_get_ticket_from_client(SSL *s, CLIENTHELLO_MSG *hello,
  *  1 on success
  *  0 on error
  */
-int tls_check_client_ems_support(SSL *s, CLIENTHELLO_MSG *hello)
+int tls_check_client_ems_support(SSL *s, const CLIENTHELLO_MSG *hello)
 {
     RAW_EXTENSION *emsext;