pcap-file: Fix memory leak in ovs_pcap_open().

In ovs_pcap_open(), we allocate memory for the 'p_file'
structure but not released when fopen fails.

Addresses-Coverity: ("Resource leak")
Fixes: b6e840a ("pcap-file: Add nanosecond resolution pcap support.")
Signed-off-by: Yunjian Wang <wangyunjian@huawei.com>
Acked-by: Aaron Conole <aconole@redhat.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

lib/pcap-file.c

@@ -89,6 +89,7 @@ ovs_pcap_open(const char *file_name, const char *mode)
                    : mode[0] == 'w' ? "writing"
                    : "appending"),
                   ovs_strerror(errno));
+        free(p_file);
         return NULL;
     }