utils: separate TLS code from netio

Knot.files

doc/man/kdig.1in

doc/man_kdig.rst

src/Makefile.am

src/utils/common/exec.c

src/utils/common/netio.c

src/utils/common/netio.h

src/utils/common/params.c

src/utils/common/params.h

src/utils/common/tls.c

src/utils/common/tls.h

src/utils/kdig/kdig_exec.c

src/utils/kdig/kdig_params.c

src/utils/kdig/kdig_params.h

src/utils/knsupdate/knsupdate_exec.c