inpcb: improve some internal function names

The 'hash' subword doesn't bring any additional information. All inpcb
lookup functions operate on hashes.

For lookup functions that work on either exact hash or wild hash just
perform s/hash_//. Rename in_pcblookup_hash() into
in_pcblookup_with_lock(), emphasizing its difference to
in_pcblookup_smr(). Rename in_pcblookup_hash_locked() to
in_pcblookup_internal(), as it doesn't return a locked inpcb and is used
only for internal purposes. Note that the IPv6 sibling of this function
already lives by name in6_pcblookup_internal(). Some future changes will
make such naming more justified.

No functional change.

Reviewed by: pouria, markj
Differential Revision: https://reviews.freebsd.org/D56482