Use only one variable denoting the size of methods arrays

Previously, there was non-consistent usage of constans SSH_KEX_METHODS,
KEX_METHODS_SIZE and of magic number 10 to reference the arrays used
for algorithm negotiation by peers. This commit settles down to the single
constant and its usage throughout the whole codebase.

Fixes T195

Signed-off-by: Jakub Jelen <jjelen@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>
(cherry picked from commit c8a621c606)

include/libssh/bind.h

@@ -22,6 +22,7 @@
 #define BIND_H_
 
 #include "libssh/priv.h"
+#include "libssh/kex.h"
 #include "libssh/session.h"
 
 struct ssh_bind_struct {
@@ -31,7 +32,7 @@ struct ssh_bind_struct {
 
   struct ssh_poll_handle_struct *poll;
   /* options */
-  char *wanted_methods[10];
+  char *wanted_methods[SSH_KEX_METHODS];
   char *banner;
   char *ecdsakey;
   char *dsakey;

include/libssh/session.h

@@ -213,7 +213,7 @@ struct ssh_session_struct {
         char *sshdir;
         char *knownhosts;
         char *global_knownhosts;
-        char *wanted_methods[10];
+        char *wanted_methods[SSH_KEX_METHODS];
         char *pubkey_accepted_types;
         char *ProxyCommand;
         char *custombanner;