tcp/dccp: Add another way to allocate local ports in connect()

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8KBYH



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Commit 07f4c900 ("tcp/dccp: try to not exhaust ip_local_port_range
in connect()") allocates even ports for connect() first while leaving
odd ports for bind() and this works well in busy servers.

But this strategy causes severe performance degradation in busy clients.
when a client has used more than half of the local ports setted in
proc/sys/net/ipv4/ip_local_port_range, if this client trys to connect
to a server again, the connect time increases rapidly since it will
traverse all the even ports though they are exhausted.

So this path provides another strategy by introducing a system option:
local_port_allocation. If it is a busy client, users should set it to 1
to use sequential allocation while it should be set to 0 in other
situations. Its default value is 0.

Signed-off-by: Lu Wei <luwei32@huawei.com>
Signed-off-by: Liu Jian <liujian56@huawei.com>

Conflicts:
	include/net/tcp.h
	net/ipv4/inet_hashtables.c
	net/ipv4/sysctl_net_ipv4.c

Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>