Consolidate network functions in salt/utils/socket_util.py

This commit moves several functions from salt/modules/network.py to
salt/utils/socket_util.py, allowing the code to be re-used to flesh out
salt/modules/win_network.py.
Replace refs to salt.utils.socket_util.ip4_addrs()

8156cb6 made this function redundant. Replaced refs with ones to
salt.utils.socket_util.ip_addrs().
Update ipcidr matcher to use network grains

This commit makes the ipcidr matcher use network grains, which
fixes #5059 (and ipcidr matching in pillar) by using the minion's IPs
rather than the master's.
rename salt.utils.socket_util to salt.utils.network

This change reflects the changed role of this module, as a more general
collection of networking functions.