Fix CI warnings

• libwget/css.c (wget_css_parse_buffer): Explicitly typecaste 'len' to int from size_t
• libwget/cookie.c (_compare_cookie2): Change datatype of 'n' from int to size_t
• libwget/cookie.c (_compare_cookie2): Typecaste 'n' to int explicitly
• libwget/http.c (_send_callback): Change datatype of 'rc' from int to ssize_t
• libwget/http.c (_recv_callback): Likewise
• libwget/http.c (wget_http_match_no_proxy): Change param name from 'no_proxies' to 'no_proxies_vec' to not to shadow global 'no_proxies'
• libwget/ssl_gnutls.c (check_ocsp_response): Explicit type conversion to unsigned int
• libwget/ssl_gnutls.c (check_ocsp_response): Delete non-reachable code
• libwget/net.c (wget_tcp_listen): Remove goto
• libwget/net.c (wget_tcp_listen): Move declaration of variable 'on' in #ifdef block where it's used
• src/options.c (set_long_option): Change datatypes of 'invert', 'char_insensitive' and 'value_present' from int to char