TCP_KEEPIDLE, TCP_KEEPINTVL and TCP_KEEPCNT not present in all operating systems

After upgrading one of my pymisp instances that runs on OpenBSD system to 2.4.160, it presented the following error:

In [1]: import pymisp
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-1-a87cdefbe0c6> in <module>
----> 1 import pymisp

~/MISP/PyMISP/lib/python3.9/site-packages/pymisp/__init__.py in <module>
     42     from .tools import update_objects  # noqa
     43
---> 44     from .api import PyMISP, register_user  # noqa
     45     from .api import PyMISP as ExpandedPyMISP  # noqa
     46     from .tools import load_warninglists  # noqa

~/MISP/PyMISP/lib/python3.9/site-packages/pymisp/api.py in <module>
     35 HTTPConnection.default_socket_options = 
HTTPConnection.default_socket_options + [
     36     (socket.SOL_SOCKET, socket.SO_KEEPALIVE, 1),  # enable keepalive
---> 37     (socket.SOL_TCP, socket.TCP_KEEPIDLE, 30),  # Start pinging after 30s of idle time
     38     (socket.SOL_TCP, socket.TCP_KEEPINTVL, 10),  # ping every 10s
     39     (socket.SOL_TCP, socket.TCP_KEEPCNT, 6)  # kill the connection if 6 ping fail  (60s total)

AttributeError: module 'socket' has no attribute 'TCP_KEEPIDLE'

The attributes TCP_KEEPIDLE, TCP_KEEPINTVL, and TCP_KEEPCNT from socket module are not present in all operating systems.

Any chance of making this code portable?

Start in pymisp/api.py at the HTTPConnection.default_socket_options setup shown in the traceback, then reproduce the import on OpenBSD or another system missing these socket attributes. Done means importing pymisp no longer raises AttributeError on operating systems that do not provide TCP_KEEPIDLE, TCP_KEEPINTVL, or TCP_KEEPCNT.