gnu: libssh: Update to 0.7.5.

* gnu/packages/ssh.scm (libssh): Update to 0.7.5.
[source](patches): New field.

gnu/packages/patches/libssh-hostname-parser-bug.patch

@@ -0,0 +1,31 @@
+Fix "Hostname" parsing in OpenSSH config files, as reported
+at <https://red.libssh.org/issues/260>.
+
+From: Niels Ole Salscheider <niels_ole@salscheider-online.de>
+Date: Mon, 8 May 2017 17:36:13 +0200
+Subject: [PATCH] Fix reading of the first parameter
+
+This is a fixup for 7b8b5eb4eac314a3a29be812bef0264c6611f6e7.
+Previously, it would return as long as the parameter was _not_ seen
+before. It also did not handle the case for the unsupported opcode (-1)
+which would cause a segfault when accessing the "seen" array.
+---
+ src/config.c | 5 +++--
+ 1 file changed, 3 insertions(+), 2 deletions(-)
+
+diff --git a/src/config.c b/src/config.c
+index 7c03b27..238a655 100644
+--- a/src/config.c
++++ b/src/config.c
+@@ -218,8 +218,9 @@ static int ssh_config_parse_line(ssh_session session, const char *line,
+   }
+ 
+   opcode = ssh_config_get_opcode(keyword);
+-  if (*parsing == 1 && opcode != SOC_HOST) {
+-      if (seen[opcode] == 0) {
++  if (*parsing == 1 && opcode != SOC_HOST &&
++      opcode > SOC_UNSUPPORTED && opcode < SOC_END) {
++      if (seen[opcode] == 1) {
+           return 0;
+       }
+       seen[opcode] = 1;