MINOR: standard.c: ipcpy() function to copy an IP address from a struct sockaddr_stor...

MINOR: standard.c: ipcpy() function to copy an IP address from a struct sockaddr_storage into an other one

The function ipcpy() simply duplicates the IP address found in one
struct sockaddr_storage into an other struct sockaddr_storage.
It also update the family on the destination structure.

Memory of destination structure must be allocated and cleared by the
caller.