*/smbclient: use the new API with SMBCCTX parameter

As a side effect, the input plugin closes the SMB/CIFS connection
after closing the file.

This solves one part of
https://github.com/MusicPlayerDaemon/MPD/issues/916

src/lib/smbclient/Context.hxx

@@ -54,6 +54,46 @@ public:
 	 * Throws on error.
 	 */
 	static SmbclientContext New();
+
+	SMBCFILE *Open(const char *fname, int flags, mode_t mode) noexcept {
+		return smbc_getFunctionOpen(ctx)(ctx, fname, flags, mode);
+	}
+
+	SMBCFILE *OpenReadOnly(const char *fname) noexcept {
+		return Open(fname, O_RDONLY, 0);
+	}
+
+	ssize_t Read(SMBCFILE *file, void *buf, size_t count) noexcept {
+		return smbc_getFunctionRead(ctx)(ctx, file, buf, count);
+	}
+
+	off_t Seek(SMBCFILE *file, off_t offset, int whence=SEEK_SET) noexcept {
+		return smbc_getFunctionLseek(ctx)(ctx, file, offset, whence);
+	}
+
+	int Stat(const char *fname, struct stat &st) noexcept {
+		return smbc_getFunctionStat(ctx)(ctx, fname, &st);
+	}
+
+	int Stat(SMBCFILE *file, struct stat &st) noexcept {
+		return smbc_getFunctionFstat(ctx)(ctx, file, &st);
+	}
+
+	void Close(SMBCFILE *file) noexcept {
+		smbc_getFunctionClose(ctx)(ctx, file);
+	}
+
+	SMBCFILE *OpenDirectory(const char *fname) noexcept {
+		return smbc_getFunctionOpendir(ctx)(ctx, fname);
+	}
+
+	void CloseDirectory(SMBCFILE *dir) noexcept {
+		smbc_getFunctionClosedir(ctx)(ctx, dir);
+	}
+
+	const struct smbc_dirent *ReadDirectory(SMBCFILE *dir) noexcept {
+		return smbc_getFunctionReaddir(ctx)(ctx, dir);
+	}
 };
 
 #endif