mount.nfs command: old glibc missing some flags

Old versions of glibc (< 2.4) have a getaddrinfo(3) implementation, but
do not include public definitions of the AI_V4MAPPED, AI_ALL, and
AI_ADDRCONFIG flags because it was believed that these flags were not
standardized.  However, these flags have standard definitions both in
POSIX 1003 and in RFCs, and were thus included in later releases of
glibc.

To allow the mount.nfs command to build on systems with these older
versions of glibc, add conditional definitions for these flags in
utils/mount/network.c.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Steve Dickson <steved@redhat.com>