misc.c : Introduce ssh_writen()

A call to write() may perform a short write on a local file.
To avoid short writes, ssh_writen() can be used.

Signed-off-by: Eshan Kelkar <eshankelkar@galorithm.com>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>
Reviewed-by: Norbert Pocs <npocs@redhat.com>

include/libssh/misc.h

@@ -120,6 +120,7 @@ int ssh_tmpname(char *name);
 char *ssh_strreplace(const char *src, const char *pattern, const char *repl);
 
 ssize_t ssh_readn(int fd, void *buf, size_t nbytes);
+ssize_t ssh_writen(int fd, const void *buf, size_t nbytes);
 
 #ifdef __cplusplus
 }