Add align_from attribute to PadField

[douniwan5788]

Checklist:

• If you are new to Scapy: I have checked CONTRIBUTING.md (esp. section submitting-pull-requests)
• I squashed commits belonging together
• I added unit tests or explained why they are not relevant
• I executed the regression tests (using cd test && ./run_tests or tox)
• If the PR is still not finished, please create a Draft Pull Request

fixes #xxx

[douniwan5788]

@gpotter2 Why would f._align be a tuple?

scapy/scapy/packet.py

Lines 2528 to 2535 in c38a5de

	# Add padding optionally
	if isinstance(f, PadField):
	if isinstance(f._align, tuple):
	pad = - cur_len % (f._align[0] * 8)
	else:
	pad = - cur_len % (f._align * 8)
	if pad:
	yield "padding", pad

[gpotter2]

Do you have a use case for this PR? Is there a protocol that needs something like that?

In any case, please add a unit test.

[douniwan5788]

Do you have a use case for this PR? Is there a protocol that needs something like that?

In any case, please add a unit test.

@gpotter2 Certainly, I will ensure to include the unit test as I work on resolving the bug. Would you kindly explain why f._align is anticipated to be a tuple?

[gpotter2]

Again,

Is there a protocol that needs something like that?

Regarding

Would you kindly explain why f._align is anticipated to be a tuple?

I honnestly have no idea :) You could try removing it and see if something breaks