Refactor http_parser code

[nashif]

Reported by Flavio Santes:

Refactor the http_parser code to meet Zephyr coding rules [1]:

• Reduce code-complexity by refactoring nested if-else and switch-case constructions to avoid the "too many leading tabs - consider code refactoring" issue
• Eliminate "macros with flow control statements"
• Eliminate "macros with complex values"
• Solve the "comparisons should place the constant on the right side of the test" issue
• Reduce the use of "macros with multiple statements"

See the attached file: checkpatch_http_parser.txt

[1] See https://gerrit.zephyrproject.org/r/#/c/3922/

(Imported from Jira ZEP-776)

[nashif]

by Flavio Santes:

• checkpatch_http_parser.txt (size: 559503)

[nashif]

by Flavio Santes:

https://gerrit.zephyrproject.org/r/#/c/4920/