Add external c declaration for c++

To make sure c++ name mangling works correctly c code should be noted "extern"

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

include/libssh/pcap.h

@@ -27,6 +27,10 @@
 #ifdef WITH_PCAP
 typedef struct ssh_pcap_context_struct* ssh_pcap_context;
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 int ssh_pcap_file_write_packet(ssh_pcap_file pcap, ssh_buffer packet, uint32_t original_len);
 
 ssh_pcap_context ssh_pcap_context_new(ssh_session session);
@@ -41,5 +45,9 @@ int ssh_pcap_context_write(ssh_pcap_context,enum ssh_pcap_direction direction, v
 		uint32_t len, uint32_t origlen);
 
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* WITH_PCAP */
 #endif /* PCAP_H_ */