smb_netaddr_type():
- if passed NULL or a string that begins with whitespace, now returns NET_NONE.
- if passed a string that begins with '@', now returns NET_UNKNOWN.
- if the user.name portion of an otherwise value Internet email address
  contains a space, now returns NET_NONE.

smb_get_net_type_by_addr()
- if passed a string that begins with '@', now returns NET_UNKNOWN.
- if passed a string with space following '@', will now return NET_UNKNOWN.
- if passed a string without a dot following '@', will never return NET_INTERNET.

Unrelated change: Add the missing FILE attribute to smb_msgattrstr()