net: utils: Add net_addr_ntop() helper function

net_addr_ntop() will convert IPv4|6 address to string form.
Renamed existing net_sprint_ip_addr_buf() to net_addr_ntop()
and adjusted parameters as per API.

Jira: ZEP-1638

Change-Id: Ia497be6bf876ca63b120529acbadcfd9162a96e3
Signed-off-by: Ravi kumar Veeramally <ravikumar.veeramally@linux.intel.com>