libcutils: Split uevent_open_socket()

The best time to attach a BPF filter to a socket is before a socket
starts receiving data. Netlink sockets start receiving data after bind()
has been called. uevent_open_socket() calls socket() and bind(). Hence
split uevent_open_socket() into two functions: one function that calls
socket() and another function that calls bind().

Bug: 203462310
Change-Id: Ia41dee4683358cf9fbb6288fad863cd4f4ac9924
Signed-off-by: Bart Van Assche <bvanassche@google.com>