configure.ac: Empty LDFLAGS before checking for libnl3
configure.ac: Empty LDFLAGS before checking for libnl3

Currently since CFLAGS are dropped if you have LDFLAGS=-pie (default on RHEL)
the rtnl_link_get_phys_port_id, rtnl_link_set_carrier and rtnl_link_get_carrier
tests always fails:

/usr/bin/ld: /tmp/ccv5GdFD.o: relocation R_X86_64_PC32 against undefined symbol
`rtnl_link_get_carrier@@libnl_3' can not be used when making a shared object;
recompile with -fPIC

This commits empty LDFLAGS before launching the 3 tests and restores it
after the tests.

Signed-off-by: Timothy Redaelli <a4b59bb75648eb5009c48ef2c8b66a57977abb22@redhat.com>
Signed-off-by: Jiri Pirko <1b548d10035ae428195c41f5d55eedb1437ccd8a@mellanox.com>

jpirko/libteam,jpirko/libteam,jpirko/libteam