inpcb: inline in_pcbconnect_setup() into in_pcbconnect()

The separation had been done back in 5200e00e7266 for the purposes of
removing a true temporary connect of an unconnected UDP socket that does
sendto(2) in 90162a4e87f0. Now, with 69c05f428714 in place, the
separation is no longer needed. There should be no functional change.

Reviewed by: markj
Differential Revision: https://reviews.freebsd.org/D49142