Registering a new protocol of type SOCK_STREAM with a protocol value other
than IPPROTO_TCP will override TCP if the application passes 0 as the protocol
to the socket() call.
socket(AF_INET, SOCK_STREAM, 0)
I guess many applications follow this syntax as they assume TCP is the default
protocol for SOCK_STREAM type.
The same holds true for SOCK_DGRAM type sockets assuing UDP as the default.

This is due to the insertion of a new inet_protosw entry into the inetsw list
of a particular type at the head of the list. inet_create() uses the first
entry in the list if a wild-card protocol is passed.

The following patch fixes the insertion of a new entry so that it is added
after the last permanent entry in the list. This makes sure that the new 
entries do not override any existing permanent entries.