smb_hfield_add_netaddr(), and by extension, the smb_hfield_netaddr() macro,

If the specified or detected net_type is not Internet, only store the address
portion of the email address in the *NETADDR hfield.
If the net_type argument is a NULL pointer, automatically add the *NETTYPE
hfield too.
New functions:
- smb_netaddr_type() - returns the string/name of a specified net_type.
- smb_get_net_type_by_addr() - parses just the network address field.
Change short/ushort's to int16_t/uint16_t's.
Remove date from copyright.