MINOR: flags/mux-fcgi: Decode FCGI connection and stream flags

The new functions fconn_show_flags() and fstrm_show_flags() decode the flags
state into a string, and are used by dev/flags:

$ /dev/flags/flags fconn 0x3100
fconn->flags = FCGI_CF_GET_VALUES | FCGI_CF_KEEP_CONN | FCGI_CF_MPXS_CONNS

./dev/flags/flags fstrm  0x3300
fstrm->flags = FCGI_SF_WANT_SHUTW | FCGI_SF_WANT_SHUTR | FCGI_SF_OUTGOING_DATA | FCGI_SF_BEGIN_SENT
2 files changed