dropbear: server support option '-T' max auth tries

Add support for '-T n' for a run-time specification for maximum number
of authentication attempts where 'n' is between 1 and compile time
option MAX_AUTH_TRIES.

A default number of tries can be specified at compile time using
'DEFAULT_AUTH_TRIES' which itself defaults to MAX_AUTH_TRIES for
backwards compatibility.

Signed-off-by: Kevin Darbyshire-Bryant <kevin@darbyshire-bryant.me.uk>

package/network/services/dropbear/patches/610-skip-default-keys-in-custom-runs.patch

@@ -1,6 +1,6 @@
 --- a/svr-runopts.c
 +++ b/svr-runopts.c
-@@ -488,6 +488,7 @@ void load_all_hostkeys() {
+@@ -505,6 +505,7 @@ void load_all_hostkeys() {
  		m_free(hostkey_file);
  	}
  
@@ -8,7 +8,7 @@
  #ifdef DROPBEAR_RSA
  	loadhostkey(RSA_PRIV_FILENAME, 0);
  #endif
-@@ -499,6 +500,7 @@ void load_all_hostkeys() {
+@@ -516,6 +517,7 @@ void load_all_hostkeys() {
  #ifdef DROPBEAR_ECDSA
  	loadhostkey(ECDSA_PRIV_FILENAME, 0);
  #endif