contrib: move net and sockaddr from internal

Knot.files

src/Makefile.am

src/contrib/net.c

src/contrib/net.h

src/contrib/sockaddr.c

src/contrib/sockaddr.h

src/knot/conf/base.c

src/knot/conf/conf.c

src/knot/ctl/knotc_main.c

src/knot/ctl/remote.c

src/knot/modules/dnsproxy.c

src/knot/modules/rosedb.c

src/knot/modules/synth_record.c

src/knot/nameserver/axfr.c

src/knot/nameserver/internet.c

src/knot/nameserver/ixfr.c

src/knot/nameserver/notify.c

src/knot/nameserver/process_answer.c

src/knot/nameserver/process_answer.h

src/knot/nameserver/process_query.c