net/libnfs: fix build error regarding "redefinition of typedef"

libnfs was redefining u_int, causing programs using libnfs to get
"error: redefinition of typedef 'u_int' is a C11 feature" errors.

Upstream PR: https://github.com/sahlberg/libnfs/pull/326

PR: 248296
Approved by: Shannon Noe <snoe925@gmail.com> (maintainer)