ext4: separate stream goal hits from s_bal_goals for better tracking

In ext4_mb_regular_allocator(), after the call to ext4_mb_find_by_goal()
fails to achieve the inode goal, allocation continues with the stream
allocation global goal. Currently, hits for both are combined in
sbi->s_bal_goals, hindering accurate optimization.

This commit separates global goal hits into sbi->s_bal_stream_goals. Since
stream allocation doesn't use ac->ac_g_ex.fe_start, set fe_start to -1.
This prevents stream allocations from being counted in s_bal_goals. Also
clear EXT4_MB_HINT_TRY_GOAL to avoid calling ext4_mb_find_by_goal again.

After adding `stream_goal_hits`, `/proc/fs/ext4/sdx/mb_stats` will show:

mballoc:
	reqs: 840347
	success: 750992
	groups_scanned: 1230506
	cr_p2_aligned_stats:
		hits: 21531
		groups_considered: 411664
		extents_scanned: 21531
		useless_loops: 0
		bad_suggestions: 6
	cr_goal_fast_stats:
		hits: 111222
		groups_considered: 1806728
		extents_scanned: 467908
		useless_loops: 0
		bad_suggestions: 13
	cr_best_avail_stats:
		hits: 36267
		groups_considered: 1817631
		extents_scanned: 156143
		useless_loops: 0
		bad_suggestions: 204
	cr_goal_slow_stats:
		hits: 106396
		groups_considered: 5671710
		extents_scanned: 22540056
		useless_loops: 123747
	cr_any_free_stats:
		hits: 138071
		groups_considered: 724692
		extents_scanned: 23615593
		useless_loops: 585
	extents_scanned: 46804261
		goal_hits: 1307
		stream_goal_hits: 236317
		len_goal_hits: 155549
		2^n_hits: 21531
		breaks: 225096
		lost: 35062
	buddies_generated: 40/40
	buddies_time_used: 48004
	preallocated: 5962467
	discarded: 4847560

Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Link: https://patch.msgid.link/20250714130327.1830534-3-libaokun1@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

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