raw ip: fix regression with multicast and RSVP

With 61f7427f02a raw sockets protosw has wildcard pr_protocol. Protocol
of a specific pcb is stored in inp_ip_p.

Reviewed by: karels
Reported by: karels
Differential revision: https://reviews.freebsd.org/D36429
Fixes: 61f7427f02a307d28af674a12c45dd546e3898e4