main/nss-pam-ldapd: enable nss module
Fixes #7946 (closed) by enabling the nss module and addressing musl compatibility.
NETDB_INTERNAL as -1 appears to be safe. It's set to -1 in glibc, musl doesn't use -1 for any other code, and the source doesn't seem to do any inequality operations on
h_errnop. I've tested the changes with openldap and haven't noticed any issues.
musl implementation: https://git.musl-libc.org/cgit/musl/tree/src/network/gethostbyname2_r.c#n11
base test image: https://gitlab.o-connor.io/nick/ldap-alpine