[ip6] remove UDP port check for messages with HostTrusted origin

[abtink]

This commit removes the checks previously performed on messages with the origin HostTrusted that are to be forwarded to the Thread mesh. This origin is used for messages generated by the OpenThread stack itself. These checks were unnecessarily restricting such messages from using Thread Control UDP port numbers (like TMF, MLE, etc.). The additional check !IsLoopbackToHostAllowed() (which is set to true by default on such messages) bypassed the entire block, preventing any functional impact.

Recent related changes (in #9437) added similar guard checks for messages with HostUntrusted origins.

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Related to #10543

[size-report]

Size Report of OpenThread

Merging #10546 into main(2cc0798).

name	branch	text	data	bss	total
ot-cli-ftd	main	467240	856	66364	534460
	#10546	467160	856	66364	534380
	+/-	-80	0	0	-80
ot-ncp-ftd	main	436316	760	61592	498668
	#10546	436236	760	61592	498588
	+/-	-80	0	0	-80
libopenthread-ftd.a	main	236580	95	40302	276977
	#10546	236496	95	40302	276893
	+/-	-84	0	0	-84
libopenthread-cli-ftd.a	main	57580	0	8075	65655
	#10546	57580	0	8075	65655
	+/-	0	0	0	0
libopenthread-ncp-ftd.a	main	32127	0	5924	38051
	#10546	32127	0	5924	38051
	+/-	0	0	0	0
ot-cli-mtd	main	365504	760	51236	417500
	#10546	365424	760	51236	417420
	+/-	-80	0	0	-80
ot-ncp-mtd	main	348220	760	46480	395460
	#10546	348124	760	46480	395364
	+/-	-96	0	0	-96
libopenthread-mtd.a	main	159003	0	25190	184193
	#10546	158919	0	25190	184109
	+/-	-84	0	0	-84
libopenthread-cli-mtd.a	main	39795	0	8059	47854
	#10546	39795	0	8059	47854
	+/-	0	0	0	0
libopenthread-ncp-mtd.a	main	25007	0	5924	30931
	#10546	25007	0	5924	30931
	+/-	0	0	0	0
ot-cli-ftd-br	main	552016	864	131228	684108
	#10546	551920	864	131228	684012
	+/-	-96	0	0	-96
libopenthread-ftd-br.a	main	325501	100	105142	430743
	#10546	325413	100	105142	430655
	+/-	-88	0	0	-88
libopenthread-cli-ftd-br.a	main	71711	0	8099	79810
	#10546	71711	0	8099	79810
	+/-	0	0	0	0
ot-rcp	main	62328	564	20636	83528
	#10546	62328	564	20636	83528
	+/-	0	0	0	0
libopenthread-rcp.a	main	9734	0	5060	14794
	#10546	9734	0	5060	14794
	+/-	0	0	0	0
libopenthread-radio.a	main	19031	0	222	19253
	#10546	19031	0	222	19253
	+/-	0	0	0	0