Fix an issue with accept_filter introduced with r261242:

Fix an issue with accept_filter introduced with r261242:

As a side effect of r261242 when using accept_filter the
first call to soisconnected() is done earlier in tcp_input()
instead of tcp_do_segment() context.  Restore the expected behaviour.

Note:  This call to soisconnected() seems to be extraneous in all
cases (with or without accept_filter).  Will be addressed in a
separate commit.

PR:			212920
Reported by:		Alexey
Tested by:              Alexey, jch
Sponsored by:           Verisign, Inc.
MFC after:		1 week