flowgrind: fix IPv4 test connection with IPv6 control connection
flowgrind: fix crash, partially revert 95863488a15f3ca49aad87533c5cb008244c47df

Commit "fix clang compile warnings", broke host parsing (see below).
This patch partially revert that commit.
However, because of other changes in this commit, this currently
will leave behind a warning, which needs to be addressed properly.

*** Error in `/home/arnd/umic-mesh/flowgrind-git/src/flowgrind': munmap_chunk(): invalid pointer: 0x0000000001a6c52c ***

Program received signal SIGABRT, Aborted.
0x00007ffff7206f79 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
56	../nptl/sysdeps/unix/sysv/linux/raise.c: Datei oder Verzeichnis nicht gefunden.
(gdb) bt
\#0  0x00007ffff7206f79 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
\#1  0x00007ffff720a388 in __GI_abort () at abort.c:89
\#2  0x00007ffff72441d4 in __libc_message (do_abort=do_abort@entry=1, fmt=fmt@entry=0x7ffff7352a10 "*** Error in `%s': %s: 0x%s ***\n")
\    at ../sysdeps/posix/libc_fatal.c:175
\#3  0x00007ffff724ef37 in malloc_printerr (action=<optimized out>, str=0x7ffff7352d90 "munmap_chunk(): invalid pointer", ptr=<optimized out>) at malloc.c:4996
\#4  0x0000000000406b17 in parse_host_option (arg=arg@entry=0x1a6c522 "localhost", endpoint=endpoint@entry=0x612118 <cflow+56>) at flowgrind.c:2294
\#5  0x0000000000406f7e in parse_flow_option_endpoint (code=<optimized out>, arg=0x1a6c522 "localhost", flow_id=0, endpoint_id=<optimized out>) at flowgrind.c:2343
\#6  0x000000000040787f in parse_cmdline (argc=argc@entry=3, argv=argv@entry=0x7fffffffdd28) at flowgrind.c:2771
\#7  0x000000000040251b in main (argc=3, argv=0x7fffffffdd28) at flowgrind.c:2911