Fix the following doxygen warnings:
src/libnetfilter_log.c:888: warning: missing title after \defgroup Printing
src/libnetfilter_log.c:216: warning: argument 'log' of command @param is not found in the argument list of nflog_fd(struct nflog_handle *h)
src/libnetfilter_log.c:216: warning: The following parameters of nflog_fd(struct nflog_handle *h) are not documented:
  parameter 'h'
src/libnetfilter_log.c:443: warning: argument 'qh' of command @param is not found in the argument list of nflog_set_mode(struct nflog_g_handle *gh, uint8_t mode, uint32_t range)
src/libnetfilter_log.c:443: warning: The following parameters of nflog_set_mode(struct nflog_g_handle *gh, uint8_t mode, uint32_t range) are not documented:
  parameter 'gh'
src/libnetfilter_log.c:824: warning: The following parameters of nflog_get_gid(struct nflog_data *nfad, uint32_t *gid) are not documented:
  parameter 'gid'
src/libnetfilter_log.c:839: warning: The following parameters of nflog_get_seq(struct nflog_data *nfad, uint32_t *seq) are not documented:
  parameter 'seq'
src/libnetfilter_log.c:856: warning: The following parameters of nflog_get_seq_global(struct nflog_data *nfad, uint32_t *seq) are not documented:
  parameter 'seq'
src/libnetfilter_log.c:809: warning: The following parameters of nflog_get_uid(struct nflog_data *nfad, uint32_t *uid) are not documented:
  parameter 'uid'