BUG/MINOR: mux-fcgi/trace: fix wrong set of trace flags in fcgi_strm_add_eom()

A typo resulted in '||' being used to concatenate trace flags, which will
only set flag of value '1' there. Noticed by clang 10 and reported in
issue #588.

No backport is needed, this trace was added in 2.2-dev.
1 file changed