Add support for INET6 addresses to the kernel code that dumps open/lock state.

PR#223036 reported that INET6 callback addresses were not printed by
nfsdumpstate(8). This kernel patch adds INET6 addresses to the dump structure,
so that nfsdumpstate(8) can print them out, post-r346190.
The patch also includes the addition of #ifdef INET, INET6 as requested
by bz@.

PR: 223036
Reviewed by: bz, rgrimes
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D19839